Dissertations / Theses on the topic 'Hydrogen atom transfers'
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1
Smith, Susan Lavinia. "Chiral selection in hydrogen atom transfer reactions." Thesis, Royal Holloway, University of London, 1986. http://repository.royalholloway.ac.uk/items/f4ae87be-b444-42db-828c-b12089967742/1/.
Abstract:
This thesis describes an attempt to demonstrate enantioselectivity in free-radical hydrogen transfer reactions and was designed to test a novel extension of the Hammond Postulate. It is proposed that the rates of two related reactions which are thermodynamically identical but kinetically distinct should differ most when the processes are thermoneutral since the transition state is remote from both reactant and product. Bysynthesis and subsequent oxidation of suitable chiral hydroxamic acids a series of persistent chiral acyl nitroxide radicals ArCON(R)O has been made. By reacting such a series of nitroxide radicals with suitable chiral benzylic alcohols ArCHOHR it was hoped that by varying the nature of, the bond strength of the alcohol would come within the compass of the 0-H bond strengths of ArCON(R)OH. It was predicted that such an alcohol should show a maximum in a plot of enantioselectivity vs. 0-H bond strength. The target molecules for this work were optically active N-alkylbenzohydroxamic acids in which the akyl substituent was both chiral and tertiary. Substitution of electron withdrawing and releasing groups, ranging from into the aroyl group of the hydroxamic acid and subsequent oxidation of the latter allowed the synthesis of radicals with varying bond strengths. UV-visible, e.s.r. and CD spectra were determined for these radicals. 0-H bond strengths of the hydroxamic acids were estimated using an e.s.r. technique which determined the equilibrium position for hydrogen atom transfer between the hydroxamic acid and a standard di-t-alkyl nitroxide radical which forms a bond of known strength to hydrogen. These estimated values range from 76 to 79 kcal mol. Enantoselectiviy was searched for in two ways. The first employed UV spectroscopy to determine the second order rate constants for the four possible reaction pairs of chiral nitroxide enantiomers with benzylic alcohol enantiomers. The second method involved reaction of racemic alcohol with chiral radical and subsequent examination of enantiomeric excess by high performance liquid chromatography (HPLC); two approaches to this are described. In the majority of cases studied, however, enantioselectivity was immeasurably small. In the case of 2-methyl-l-phenylpropan-l-ol, a small enantiomeric excess was observed but further work is needed to substantiate these results. Small chiral discriminations were observed in the oxidation reactions of only one alcohol. These results were insufficient to investigate the extension of the Hammond Postulate as originally planned.
2
Elayoubi, Mustapha. "Transfert d'atomes d'hydrogène vers la cathode d'un arc réducteur de composition argon-hydrogène /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1989. http://theses.uqac.ca.
3
Pillai, Jayasheela. "Heterocycle synthesis by hydrogen atom transfer and cyclisation." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298644.
4
Harvey, Erica Lyn Gray Harry B. "Photochemical hydrogen atom transfer reactions of binuclear platinum complexes /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-06112007-134908.
5
Beaufils, Florent. "Recent developments in radical-mediated hydrogen atom transfer reaction /." [S.l.] : [s.n.], 2004. http://www.zb.unibe.ch/download/eldiss/04beaufils_f.pdf.
6
Bouchet, Damien. "Applications de l'organocatalyse asymétrique et de la photocatalyse aux additions nucléophiles sur des dérivés α,β-insaturés électroappauvris." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASF001.
Abstract:
Les additions nucléophiles sur les accepteurs de Michael comptent parmi les réactions les plus fondamentales de la chimie organique. Elles n'ont eu de cesse d'être revisitées, notamment au gré de l'emploi de dérivés α,β-insaturés peu conventionnels. La catalyse permet de démultiplier leurs potentialités tout en s'inscrivant dans une démarche plus respectueuse de l'environnement. Aussi, cette thèse s'ouvre par une partie dédiée à l'organocatalyse asymétrique. Le premier chapitre relate le développement d'une cycloaddition (4 + 2) asymétrique promue par des isothiourées et permettant la synthèse d'anti-2,3-dihydrothiopyranones. La réactivité singulière des thiochalcones, utilisées pour la première fois en tant qu'accepteurs de Michael, y est mise en exergue. Un deuxième chapitre est consacré à une cycloaddition (3 + 2) entre des quinones diimines et des énecarbamates médiée par les acides phosphoriques chiraux. Elle a conduit à des indolines 2,3-disubstituées. Étonnamment, des produits acycliques de ζ-amination ont été formés en étendant cette transformation aux triénecarbamates. Ils résultent d'une addition 1,6 sur l'azote des quinones diimines. Afin d'optimiser la stéréosélectivité de cette transformation, nous nous sommes tournés vers l'intelligence artificielle. Une seconde partie porte sur une désaromatisation photocatalytique d'indoles électoappauvris en C3 par C2-acylation. Elle repose sur l'addition de radicaux générés à partir d'aldéhydes par un HAT direct opéré par le TBADT, un polyoxométallateNucleophilic additions to Michael acceptors constitute one of the most fundamental class of reactions in organic chemistry. They have been frequently revisited using unconventional α,β-unsaturated derivatives. Catalysis drastically increases their potential while falling within an environmentally-friendly approach. Hence, this manuscript begins with a first part devoted to asymmetric organocatalysis. The opening chapter focuses on the development of an asymmetric (4 + 2)-cycloaddition promoted by isothioureas. It enabled the synthesis of anti-2,3-dihydrothiopyranones while showcasing the peculiar reactivity of thiochalcones. They were used, for the first time, as Micheal acceptors. The second chapter is dedicated to a (3 + 2)-cycloaddition between quinones diimines and enecarbamates. It led to 2,3-disubstituted indolines. Surprisingly, ζ-amination acyclic products were obtained when we extended this transformation to trienecarbamates. They resulted from a 1,6-addition on the nitrogen of quinone diimines. Aiming to optimize the stereoselectivity of this transformation, we turned our attention towards artificial intelligence. A second part deals with a photocatalytic dearomatization of indoles bearing an electron-withdrawing group at C3 position via their C2-acylation. It relied on the addition of acyl radical species generated from aldehydes through a HAT mediated by a polyoxometalate: the TBADT
7
Roth, Justine P. "Intrinsic and thermodynamic influences on hydrogen atom transfer reactions involving transition metal complexes /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/11602.
8
Støchkel, Kristian. "Electron-transfer processes in fast ion-atom collisions." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-732.
9
Asous, Nadia K. "Hydrogen Atom Transfer Reactivity of Bio-inspired Unsymmetrical Dicopper– oxo/peroxo Complexes." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1533245264093817.
10
Anderson, Andrea H. "Mechanistic Studies on the Monoamine Oxidase B Catalyzed Oxidation of 1,4-Disubstituted Tetrahydropyridine Derivatives." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30566.
Abstract:
The flavin-containing monoamine oxidases (MAO) A and B catalyze the oxidative deamination of primary and secondary amines. The overall process involves a two electron oxidation of the amine to the iminium with concomitantreduction of the flavin. Based on extensive studies with a variety of chemical probes, Silverman and colleagues have proposed a catalytic pathway for the processing of amine substrates and inactivators by MAO-B that is initiated by a single electron transfer (SET) step from the nitrogen lone pair to the oxidized flavin followed by a-proton loss from
the resulting amine radical cation that leads to a carbon radical. Subsequent transfer of the second electron leads to the reduced flavin and the iminium product. In the case of
N-cyclopropylamines, the initially formed amine radical cation is proposed to undergo rapid ring opening to form a highly reactive primary carbon centered radical that is thought to be responsible for inactivation of the enzyme. In
this thesis we have exploited the unique substrate and inactivator properties of 1,4-disubstituted tetrahydropyridine derivatives to probe the mechanism of MAO-B catalysis. Reports of the parkinsonian inducing
neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a structurally unique substrate of MAO-B initiated these studies. Consistent with the SET pathway, the N-cyclopropyl analog of MPTP proved to be an efficient time and concentration dependent inactivator but not a substrate of MAO-B. On the other hand, the 4-benzyl-1-cyclopropyl analog is both a substrate and inactivator of MAO-B. These properties may not be consistent with the
obligatory formation of a cyclopropylaminyl radicalcation intermediate. In an attempt to gain further insight into the mechanism associated with the MAO catalyzed oxidation of 1,4-disubstituted tetrahydropyridines, deuterium isotope effects studies on both the substrate and inactivation properties of the 4-benzyl-1- cyclopropyl derivative were undertaken. A series of 1-methyl- and 1-cyclopropyltetrahydropyridine derivatives bearing various heteroaro-matic groups at C-4 also have been examined. The MAO-B substrate properties, inactivator properties and partition ratios for these compounds together with preliminary results from chemical model studies are discussed in terms of the MAO-B catalytic pathway.Ph. D.
11
Quichaud, Viviane. "Etude des processus elementaires : de synthese de la molecule no, en post-decharge en ecoulement, de collisions titane-gaz rares, titane-molecules, par perturbation laser resolue en temps." Paris 6, 1987. http://www.theses.fr/1987PA066135.
Abstract:
I. Etude de la preparation des etats excites de no dans un dispositif de post-decharge en ecoulement a partir de n::(2) excite (prepare par transfert d'excitation a partir d'atomes ar metastables dans une decharge basse pression) et de o (obtenu par dissociation de o::(2) dans une decharge de he). Observation d'une emission intense des bandes gamma de no, qui implique un etat a courte duree de vie (b) de n::(2) et le premier etat metastable de o. Ii. Analyse des processus d'extinction et de transfert d'excitation a partir d'etats a courte duree de vie de ti (crees dans un dispositif a cathode creuse) lors de collisions avec des gaz rares (ar, ne, he) et des molecules (n::(2),h::(2)). Ces experiences permettent l'etude de cinetiques de reactions elementaires au sein d'un plasma basse pression ensemence de vapeurs metalliques, a l'aide du dispositif de post-decharge en ecoulement
12
Wu, Adam Cheng-Hong. "Tunneling in hydrogen atom transfer reactions of ruthenium complexes, nitroxyl radicals, and hydroxylamines /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/8562.
13
Mader, Elizabeth Anne. "Hydrogen atom transfer reactions of iron and cobalt tris alpha-diimines : a study of intrinsic and thermodynamic effects /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8617.
14
Eschlimann, Alain. "Photo-décomposition de l'acide formique et exploitation de la réactivité des anions phosphorés en chimie radicalaire." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC262.
Abstract:
Les recherches présentées dans ce manuscrit s’articulent autour de deux parties distinctes. La première partie concerne une étude mécanistique de la réaction de décomposition de l’acide formique (AF) photocatalysé par le Tetra-n-ButylAmmonium DecaTungstate (TBADT) et explore la réactivité de ce photocatalyseur envers l’AF. La deuxième partie de ces travaux se focalise sur l’étude de la réactivité radicalaire d’anions phosphorés et de leurs analogues chalcogénés. Dans un premier temps, nous nous sommes intéressés à exploiter la réactivité de phosphures-borane et des anions d’oxydes de phosphine pour la formation de liaisons C-P par photo-induction dans le visible. Dans un second temps, nous avons exploré la réactivité radicalaire et ionique des phosphures-borane chalcogénés, par une étude de leur structure et de leur réactivité. Ces propriétés ont été mises en application dans le cadre de réactions de photo-polymérisation radicalaire et de réduction de composés électrophilesThis dissertation is organized in two distinct parts. The first one is a mechanistic investigation of the photocatalyzed reaction of decomposition of formic acid (AF) under mild conditions using Tetra-n-ButylAmmonium DecaTungstate (TBADT). The second part of this work revolve around the use and study of the radical reactivity of phosphorous anions and their chalcogenated analogues. Firstly, we used the radical reactivity of phosphido-borane and phosphine oxide anions for the formation of C-P bonds. In a last part, we explored the radical and ionic reactivity of chalcogenated phosphido-borane, by studying their structure and reactivity. These properties has been applied to radical photo-polymerization reactions and for the reduction of electrophiles
15
Jenkinson, Richard I. "The quantum dynamics of proton transfer in the hydrogen bond." Thesis, University of Nottingham, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299563.
16
So, Eric. "Interaction of Rydberg hydrogen atoms with metal surfaces." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:53984973-1766-45cc-8bcf-055be714ed73.
Abstract:
This thesis presents a theoretical and experimental investigation of the interaction of electronically excited Rydberg hydrogen atoms with metal surfaces and the associated charge-transfer process. As a Rydberg atom approaches a metal surface, the energies of the Rydberg states are perturbed by the surface potential generated by the image charges of the Rydberg electron and core. At small atom-surface separations, the Rydberg atom may be ionised by resonant charge transfer of the Rydberg electron to the continuum of delocalised unoccupied metal states, with which the Rydberg electron is degenerate in energy. Typically, this ‘surface ionisation’ can be measured by extracting the remaining positively charged ion-cores with externally applied electric fields. By applying various levels of theory, from classical to fully time-dependent quantum calculations, this thesis explores various experimentally relevant effects on the charge-transfer process, such as the magnitude and direction of the externally applied electric field, the atom collisional velocity, the presence of local surface stray fields and electronically structured surfaces. The theoretical results give insight into the previous experimental work carried out for the xenon atom and hydrogen molecule, and point out some of the fundamental differences from the hydrogen atom system. Experiments involving Rydberg hydrogen atoms incident on an atomically flat gold surface, a rough machined aluminium surface and a single crystal copper (100) surface are presented, providing for the first time the opportunity to make a quantitative comparison of theory and experiments. The ability to control the critical distance at which charge-transfer occurs is demonstrated by using Rydberg states of varying dimensions and collisional velocities. By changing the collisional angle of the incident Rydberg beam, the effect of Rydberg trajectory is also investigated. By manipulating the polarisation of the Rydberg electron with electric fields, genuine control over the orientation of the electron density distribution in the charge-transfer process is demonstrated. This property was predicted by the theory and should be unique to the hydrogen atom due to its intrinsic symmetry. By reversing the direction of the electric field with respect to the metal surface, electrons rather than positive ions are detected, with ionisation dynamics that appear to be very different, as predicted by quantum calculations. Experiments involving the single crystal Cu(100) surface also suggests possible resonance effects from image states embedded in the projected bandgap which are shown from quantum calculations to play an important role in the surface charge transfer of electronically structured metal substrates. The experimental technique developed in this work provides some exciting future applications to study quantum confinement effects with thin films, nanoparticles and other bandgap surfaces. The ability to control the Rydberg orbital size, electronic energy, collisional velocity and orientation in the charge-transfer process will provide novel ways of probing the surface’s electronic and physical structure, as well as being a valuable feature in offering new opportunities for controlling reactive processes at metallic surfaces.
17
Ganeshalingam, Sashikesh. "Charge transfer of Rydberg hydrogen molecules and atoms at doped silicon surfaces." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:9f1f6bb6-47a0-47f6-ad55-52f416d08815.
Abstract:
The work of this thesis focuses on the interaction of high Rydberg states of hydrogen molecules and atoms with various doped Si semiconductor surfaces with the results compared with those obtained with an atomically flat gold surface. The major part of the thesis was carried out using para-H₂ molecular Rydberg states with principal quantum number n = 17 - 21 and core rotational quantum number N⁺ = 2. Subsequently, this study was continued using H atomic Rydberg states with principal quantum number n = 29 - 34. The high Rydberg states have been produced using two-step laser excitation. For close Rydberg surface separation (< 6 n² a.u.), the Rydberg states may be ionized due to an attractive surface potential experienced by the Rydberg electron, and the remaining ion core may be detected by applying an external electric field. An efficient ion detectability method is introduced to compare the many surface ionization profiles quantitatively. The p-type doped Si surfaces enhance the detected ion-signal more than the n-type doped Si surfaces due to the presence of widely distributed positive dopant charge fields in the p-type doped Si surfaces. As the dopant density increases, the area sampled by the resultant ions becomes effectively more neutral, and the decay rate of the potential from the surface dopant charge with distance from the surface becomes more rapid. Therefore, the minimum ionization distance is also reduced with increasing dopant density. It is found that the detected ion-signal decreases with increasing dopant density of both p- and n- type doped Si surfaces. The higher-n Rydberg states have shown higher ion detectability than that of lower-n Rydberg states and this variation also becomes smaller when increasing the dopant density. Experiments involving H2 Rydberg molecules incident on various doped Si surfaces in the presence of a Stark field at the point of excitation are also presented here. The surface ionization profiles produced via both electron and ion detection schemes are measured by changing the Stark polarization. Positive surface dopant charges oppose production of backscattered electrons and negative surface dopant charges enhance the electron-signal. For the electron detection scheme, lightly doped n-type Si surfaces show higher detectability but in the case of p-type Si surfaces the more heavily doped Si surfaces give a higher detected signal. This different behaviour of the detected ion or electron signal implies a different production mechanism. Theoretical trajectory simulations were also carried out based on a new 2D surface potential model. The results qualitatively agree with the experimental results and explain the changes of the surface ionization profiles between the various dopant types and dopant densities of the Si surfaces.
18
Grimm, Michelle L. "Development of New N-Cyclopropyl Based Electron Transfer Probes for Cytochrome P-450 and Monoamine Oxidase Catalyzed Reactions." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/37919.
Abstract:
The recent upsurge of degenerative diseases believed to be the result of oxidative stress has sparked an increased interest in utilizing the fundamental principles of physical organic chemistry to understand biological problems. Enzyme pathways can pose several experimental complications due to their complexity, therefore the small molecule probe approach can be utilized in an attempt understand the more complex enzyme mechanisms. The work described in this dissertation focuses on the use of N-cyclopropyl amines that have been used as probes to study the mechanism of monoamine oxidase (MAO) and cytochrome P-450 (cP-450).
A photochemical model study of benzophenone triplet (3BP) with the MAO-B substrate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and two of itâ s derivatives, 1-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine and (+/-)-[trans-2-phenylcyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine is presented in Chapter 2. The barrier for ring opening of aminyl radical cations derived from N-cyclopropyl derivatives of tertiary amines (such as MPTP) is expected to be low. Reactions of 3BP with all three compounds are very similar. The results suggest that the reaction between benzophenone triplet and tertiary aliphatic amines proceed via a simple hydrogen atom transfer reaction. Additionally these model examinations provide evidence that oxidations of N-cyclopropyl derivatives of MPTP catalyzed by MAO-B may not be consistent with a pure SET pathway.
The chemistry of N-cyclopropyl amines has been used to study the mechanism of amine oxidations by cP-450. Until recently, the rate constant for these ring opening reactions has not been reported. Direct electrochemical examinations of N-cyclopropyl-N-methylaniline showed that the radical cation undergoes a unimolecular rearrangement consistent with a cyclopropyl ring opening reaction. Examination of both the direct and indirect electrochemical data showed that the oxidation potential N-cyclopropyl-N-methylaniline to be +0.528 V (0.1 M Ag+/Ag), and rate constant for ring opening of 4.1 x 104 s-1. These results are best explained by two phenomena: (i) a resonance effect in which the spin and charge of the radical cation in the ring closed form is delocalized into the benzene ring hindering the overall rate of the ring opening reaction, and/or (ii) the lowest energy conformation of the molecule does not meet the stereoelectronic requirements for a ring opening pathway. Therefore a new series of spiro cyclopropanes were designed to lock the cyclopropyl group into the appropriate bisected conformation. The electrochemical results reported herein show that the rate constant for ring opening of 1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] and 6'-chloro-1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] are 3.5 x 102 s-1 and 4.1 x 102 s-1 with redox potentials of 0.3 V and 0.366 V respectively. In order to examine a potential resonance effect a derivative of N-methyl-N-cyclopropylaniline was synthesized to provide a driving force for the ring opening reaction thereby accelerating the overall rate of the ring opening pathway. The electrochemical results show that the rate constant for ring opening of 4-chloro-N-methyl-N-(2-phenylcyclopropyl)aniline to be 1.7 x 108 s-1 . The formal oxidation potential (E°OX) of this substrate was determined to be 0.53 V.
The lowered redox potentials of 1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] and 6'-chloro-1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] can be directly attributed to the electron donating character of the ortho alkyl group of the quinoline base structure of these spiro derivatives, and therefore the relative energy of the ring closed radical cations directly affects the rate of ring opening reactions. The relief of ring strain coupled with the formation of the highly resonance stabilized benzylic radical explains the rate increase for the ring opening reaction of 4-chloro-N-methyl-N-(2-phenylcyclopropyl)aniline.Ph. D.
19
Raston, Paul L. "Spectroscopy and dynamics of rare gas and chlorine atoms in solid hydrogen." Laramie, Wyo. : University of Wyoming, 2007. http://proquest.umi.com/pqdweb?did=1338905001&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
20
Paradzinsky, Mark. "Hydrogen Abstraction by the Nighttime Atmospheric Detergent NO3·: Fundamental Principles." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103783.
Abstract:
The nitrate radical (NO3·) was first identified as early as the 1881, but its role in atmospheric oxidation has only been identified within recent decades. Due to its high one-electron reduction potential and its reactivity toward a diverse set of substrates, it dominates nighttime atmospheric oxidation and has since been the subject of much work. Despite this, studies on NO3· hydrogen atom transfer reactions have been somewhat neglected in favor of its more reactive oxidative pathways.
The first section of the dissertation will highlight the role of substrate structure, solvent effects, and the presence of a polar transition state on NO3· hydrogen abstractions from alcohols, alkanes, and ethers. In this work the acquisition of absolute rate constants from previously unexamined substrates was analyzed alongside a curated list of common organic pollutants degraded through hydrogen atom abstraction. It was found that NO3· reacts with low selectivity through an early polarized transition state with a modest degree of charge transfer. Compared to the gas-phase, condensed-phase reactions experience rate enhancement—consistent with Kirkwood theory—as a result of the polarized transition state.
These insights are then applied to abstractions by NO3· from carboxylic acids in the next section. It was found that the rate constants for abstraction of α-carbons were diminished through induction by the adjacent carbonyl compared to the activation seen for the aforementioned substrates. The deactivation of abstraction by the carbonyl was found to be dramatically reduced as the substrate's alkyl chain was lengthened and/or branched. This apparent change in mechanism coincides with hydrogen abstraction of the alkyl chain for sufficiently large carboxylic acids and rules out the possibility of concerted bond breaking elsewhere in the molecule.
Finally, the dissertation will cover some additional projects related to the overall nature of the work including examination of the kinetics of radical clock systems when complexed with metal ions and the examination of a highly oxidative biosourced monomer.Doctor of Philosophy
The nitrate radical (NO3·) was first identified as early as the 1881, but its role in the breakdown of atmospheric pollutants has only been identified within recent decades. Operating primarily at night, NO3· serves as a major atmospheric oxidant—it breaks down pollutants by reactions that involve the removal of electrons from those substrates. This chemistry is particularly important in understanding the consequences of an increasingly industrialized world and the subsequent short-term health and environmental implications. Geographically, these reactions will occur in large concentrations near locations that contribute greatly to atmospheric pollution, such as above coal-powered plants, heavily industrialized areas, above the canopy of large forests, and immediately behind the engines of airplanes as they move through the sky. The proximity of these locations to large population centers has caused the pollutants to greatly impact human health. These contaminants have been linked to several of the leading global causes of death, such as ischemic heart disease, stroke, and respiratory illnesses. The first section of the dissertation will focus on the role of pollutant structure, the medium in which the reaction occurs, and the development of a charged complex when NO3· reacts with alcohols, alkanes, and ethers. These substrates are often found as the result of incomplete combustion when burning fuel or as products of even more sustainable biodiesels. In this work the exact rate constants were found for substrates that were previously unexamined and compared with similar known reaction rates. It was found that NO3· has a low preference for what it reacts with and passes through a modestly charged complex early in the reaction. Compared to gaseous reactions, reactions in a liquid environment proceed faster due to the formation of a charged complex. This was then applied to reactions with carboxylic acids in the next section. Carboxylic acids are often found in large concentrations above the canopy of large forests resulting from the oxidation of isoprenes that are naturally released from broad-leaf trees. It was found that these reactions were slower than reactions with alkanes as the development of the charged complex was inhibited due to the presence of an adjacent dipole. When the carboxylic acid was longer and/or more branched, the formation of the charged complex was no longer inhibited as the reaction site moved further from the dipole. A change in reaction pathway was observed when the acids were sufficiently large. This ruled out the possibility of the reaction occurring simultaneously with a fracturing and rearrangement elsewhere. Finally, the dissertation will cover some additional projects that share some overlap with the work already described including the study of the rates of radical clock systems in the presence of metal ions and the study of naturally sourced monomers that are prone to losing electrons.
21
Chirra, Dinakar Hariharasudhan. "NANOSCALE FUNCTIONALIZATION AND CHARACTERIZATION OF SURFACES WITH HYDROGEL PATTERNS AND BIOMOLECULES." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/60.
Abstract:
The advent of numerous tools, ease of techniques, and concepts related to nanotechnology, in combination with functionalization via simple chemistry has made gold important for various biomedical applications. In this dissertation, the development and characterization of planar gold surfaces with responsive hydrogel patterns for rapid point of care sensing and the functionalization of gold nanoparticles for drug delivery are highlighted.
Biomedical micro- and nanoscale devices that are spatially functionalized with intelligent hydrogels are typically fabricated using conventional UV-lithography. Herein, precise 3-D hydrogel patterns made up of temperature responsive crosslinked poly(N-isopropylacrylamide) over gold were synthesized. The XY control of the hydrogel was achieved using microcontact printing, while thickness control was achieved using atom transfer radical polymerization (ATRP). Atomic force microscopy analysis showed that to the ATRP reaction time governed the pattern growth. The temperature dependent swelling ratio was tailored by tuning the mesh size of the hydrogel. While nanopatterns exhibited a broad lower critical solution temperature (LCST) transition, surface roughness showed a sharp LCST transition. Quartz crystal microbalance with dissipation showed rapid response behavior of the thin films, which makes them applicable as functional components in biomedical devices.
The easy synthesis, relative biocompatibility, inertness, and easy functionalization of gold nanoparticles (GNPs) have made them useful for various biomedical applications. Although ATRP can be successfully carried out over GNPs, the yield of stable solution based GNPs for biomedical applications prove to be low. As an alternative approach, a novel method of ISOlating, FUnctionalizing, and REleasing nanoparticles (ISOFURE) was proposed. Biodegradable poly(β-amino ester) hydrogels were used to synthesize ISOFURE-GNP composites. ATRP was performed inside the composite, and the final hydrogel coated GNPs were released via matrix degradation. Response analysis confirmed that the ISOFURE method led to the increased stability and yield of the hydrogel coated ISOFURE-GNPs. The ISOFURE protocol was also utilized in functionalizing GNPs with enzyme catalase in the absence of a stabilizing reagent. Biotin-streptavidin affinity was used as the bioconjugation method. Activity analysis of the conjugated enzyme showed that the ISOFURE-GNPs showed enhanced biomolecular loading relative to solution based stabilizing reagent passivated GNPs.
22
Nakafuku, Kohki Mitchell. "Radical Relay Strategies for C-H Functionalization of Alcohols." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555519365273501.
23
Kohlhoff, Mike. "Developing surface ionisation charge-transfer dynamics of hydrogen Rydberg atoms into an energy-resolved probe of surfaces." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:dd2cd7ea-689a-4707-88e3-0d5f0eb01e88.
Abstract:
As a Rydberg atom approaches a surface, it will eventually undergo ionisation by charge transfer into the surface at a distance of about 100nm (for principal quantum numbers n > 20). The dynamics of this process are sensitive to the electronic and geometric structure of the surface and can display signature characteristics. As such, Rydberg atoms can be used to probe image-charge effects or to measure small superficial electric stray or patch fields. The charge-transfer process can be in resonance between the Rydberg energies and the energetically discrete surface states (image states) in a bandgap. Surface ionisation of Rydberg atoms is investigated for graphene, which is a zero-bandgap semiconductor and can behave either as a metal or a semiconductor. The charge-transfer dynamics observed here exhibit the characteristics of a metal with enlarged ion detection efficiency compared to a copper sample -- in accordance with other properties of graphene, such as conductivity, that are enlarged compared with a regular metal. For hydrogen Rydberg atoms, surface ionisation is detected for distances up to 10 µm, with a double series of high-lying image states extending far from the graphene film possibly creating a quasi-continuum at large atom-surface separations with a density of states beyond the resolution of the Rydberg states from n=20 to 40. The resonance behaviour for graphene is explored with a range of Rydberg H-atom collisional velocities whose effect on the charge transfer process introduces an additional handle on the probing of electronically discrete features of a surface. A wave-packet propagation study of a hydrogen atom incident at a free-metal surface up to n=20 displays shifts in ionisation towards greater distances and over a narrower range when acceleration of the ion core is not included. The thereby significantly reduced effect of the collisional velocity of Rydberg surface ionisation is also observed in an experimental study with a limited velocity range available from supersonic expansion directed at a gold sample. This either suggests that the range of Rydberg projectile velocities is to narrow to have observable effects or that a pronounced velocity dependency is merely detected for distinct electronic resonances. With the aim to further elucidate the velocity dependence and to prospectively remove ambiguities that arise from the nature of the experiment, a chip-based decelerator is constructed and integrated into the experimental apparatus for the first time. Within the constraints of the design and the existing apparatus, the chip device is not able to produce sufficient densities of decelerated particles to be employed in surface-ionisation experiments. Extensive modelling of the deceleration process indicates that modifications to the existing design and the experimental apparatus could achieve a tunable-velocity source of hydrogen Rydberg atoms with greatly enhanced densities for future investigations.
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Jaïdane, Nejmeddine. "Etude du transfert de charge entre des atomes de soufre et des protons." Paris 7, 1987. http://www.theses.fr/1987PA077121.
Abstract:
Calculs scf et ci des courbes de potentiel du systeme s+h**(+) dans les symetriplets pi et delta internenant dans la reaction, avec des orbitales moleculaires occupees representees par des orbitales atomiques polarisees et des orbitales moleculaires virtuelles donnees par la projection d'orbitales atomiques orthogonalement aux orbitales occupees. Traitement de la dynamique de l'echange de charge dans une representation diabatique ou les couplages radiaux sont nuls et l'echange de charge est induit par des couplages de type electronique. Construction d'une representation effective de dimension reduite au nombre des voies ouvertes; calcul des couplages radiaux. Resolution des equations de collision par un traitement quantique dans chaque symetrie; deduction de la constante de vitesse
25
Mitroka, Susan M. "Modulation of Hydroxyl Radical Reactivity and Radical Degradation of High Density Polyethylene." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77137.
Abstract:
Oxidative processes are linked to a number of major disease states as well as the breakdown of many materials. Of particular importance are reactive oxygen species (ROS), as they are known to be endogenously produced in biological systems as well as exogenously produced through a variety of different means. In hopes of better understanding what controls the behavior of ROS, researchers have studied radical chemistry on a fundamental level. Fundamental knowledge of what contributes to oxidative processes can be extrapolated to more complex biological or macromolecular systems.
Fundamental concepts and applied data (i.e. interaction of ROS with polymers, biomolecules, etc.) are critical to understanding the reactivity of ROS. A detailed review of the literature, focusing primarily on the hydroxyl radical (HO•) and hydrogen atom (H•) abstraction reactions, is presented in Chapter 1. Also reviewed herein is the literature concerning high density polyethylene (HDPE) degradation. Exposure to treated water systems is known to greatly reduce the lifetime of HDPE pipe. While there is no consensus on what leads to HDPE breakdown, evidence suggests oxidative processes are at play.
The research which follows in Chapter 2 focuses on the reactivity of the hydroxyl radical and how it is controlled by its environment. The HO• has been thought to react instantaneously, approaching the diffusion controlled rate and showing little to no selectivity. Both experimental and calculational evidence suggest that some of the previous assumptions regarding hydroxyl radical reactivity are wrong and that it is decidedly less reactive in an aprotic polar solvent than in aqueous solution. These findings are explained on the basis of a polarized transition state that can be stabilized via the hydrogen bonding afforded by water. Experimental and calculational evidence also suggest that the degree of polarization in the transition state will determine the magnitude of this solvent effect.
Chapter 3 discusses the results of HDPE degradation studies. While HDPE is an extremely stable polymer, exposure to chlorinated aqueous conditions severely reduces the lifetime of HDPE pipes. While much research exists detailing the mechanical breakdown and failure of these pipes under said conditions, a gap still exists in defining the species responsible or mechanism for this degradation. Experimental evidence put forth in this dissertation suggests that this is due to an auto-oxidative process initiated by free radicals in the chlorinated aqueous solution and propagated through singlet oxygen from the environment. A mechanism for HDPE degradation is proposed and discussed. Additionally two small molecules, 2,3-dichloro-2-methylbutane and 3-chloro-1,1-di-methylpropanol, have been suggested as HDPE byproducts. While the mechanism of formation for these products is still elusive, evidence concerning their identification and production in HDPE and PE oligomers is discussed.
Finally, Chapter 4 deals with concluding remarks of the aforementioned work. Future work needed to enhance and further the results published herein is also addressed.Ph. D.
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Gibbard, Jemma. "Rydberg ionisation into confined and discrete systems." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:631cf025-c29c-4c46-a219-6f2ae02df4ad.
Abstract:
The energy levels of a hydrogen Rydberg atom approaching a metallic structure are perturbed by the image-charge interaction with the surface. At small atom-surface separations surface ionisation of the Rydberg electron can occur, whereby the electron is transferred to a metal-localised state. In previous studies investigating surface ionisation at bulk metallic surfaces, this state has been part of a conduction band; however this thesis focuses on metallic and structured surfaces where the Rydberg electron transfers into a discrete image-state or hybrid 'well-image state'. The surface ionisation of hydrogen Rydberg atoms at a Cu(100) projected band-gap surface is investigated experimentally and theoretically. Experimentally, the surface ionisation of an incident beam of hydrogen Rydberg atoms is measured by extraction of the resulting ions. Resonance-enhanced charge transfer is seen for hydrogen Rydberg states that are degenerate with copper-localised image-states. A wavepacket propagation study shows that for on-resonance states the maximum in the surface-ionisation probability is shifted away from the surface by decreasing the collisional velocity. The discrete hybrid 'well-image states' localised along the surface normal of a thin-film change energy with thin-film thickness. The interaction of hydrogen Rydberg atoms with iron thin films deposited on an insulating substrate is investigated. The preference for electron penetration along the surface normal is seen by the resonance-enhancement of charge transfer at energies where the Rydberg state and well-image state are degenerate. By changing the thickness of the thin film, by in situ depositions, the energies of the well-image state are altered and the Rydberg n-values at which resonances occur, change. At a thickness of 30-monolayer the energetic spacings between the well-image states and the Rydberg states become comparable, and the single well-image state resolution is lost. A wavepacket-propagation study investigates the interaction of a nanoparticle and low-n hydrogen Rydberg atoms. The nanoparticle has a fully confined potential which at small radii yields well-spaced, fully discrete well-image states. Resonance-enhanced charge transfer occurs when the Rydberg state and the nanoparticle well-image state energy levels are degenerate. However, when there is poor energy matching between the nanoparticle well-image state and the Rydberg atom, no charge transfer is seen i.e. surface ionisation does not occur. Overall, the work presented here demonstrates the capability of Rydberg-surface studies to identify discrete, high-lying energy levels at specific surfaces.
27
Cecchini, Chiara. "Late Transition Metal-Oxo complexes: Synthesis, and Biorelevant Reactivity." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11249/.
Abstract:
High-valent terminal metal-oxygen adducts are supposed to be potent oxidising intermediates in enzymatic catalyses. In contrast to those from groups 6-8, oxidants that contain late transition metals (Co, Ni, Cu) are poorly understood. Because of their high reactivity, only a few examples of these compounds have been observed. The aim of this project was to investigate the reactivity of high-valent Ni(III) complexes, containing a monodentate oxygen-donor ligands, in hydrogen atom abstraction (HAA) and oxygen atom transfer (OAT) reactions which are typical of biological high-valent metal-oxygen species. Particularly, the Ni(III) complexes were generated in situ, at low temperature, from the oxidation of the Ni(II) species.The nickel complexes studied during this work were supported by tridentate ligands, with a strong σ-donating ability and exceedingly resistant to several common degradation pathways. These complexes vary based on the monodentate group in the fourth coordination position site, which can be neutral or anionic. In particular, we prepared four different Ni(III) complexes [NiIII(pyN2Me2)(OCO2H)] (12), [NiIII(pyN2Me2)(ONO2)] (14), [NiIII(pyN2Me2)(OC(O)CH3)] (18) and [NiIII(pyN2Me2)(OC(O)H)] (25). They feature a bicarbonate (-OCO2H), nitrate (-ONO2), acetate (-OC(O)CH3) and formate (-OC(O)H) group, respectively.HAA and OAT reactions were performed by adding 2,6-di-tert-butylphenol (2,6-DTBP) at -40°C, and triphenylphosphine (PPh3) at -80°C, to the in situ generated Ni(III) complexes, respectively. These reactions were carried out by adding 7 to 500 equivalents of substrate, in order to ensure pseudo-first order conditions. Since, the reactivity of the Ni(III) complex featured by the bicarbonate group has been studied in a previous work, we only investigated that of the species bearing the nitrate, acetate and formate ligand. Finally we compared the value of the reaction rate of all the four species in the HAA and OAT reactions.
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Monte, Pérez Inés [Verfasser], Kallol [Gutachter] Ray, and Christian [Gutachter] Limberg. "Bioinspired oxidation reactions involving mono- and poly-nuclear transition metal complexes : hydrogen atom abstraction and group transfer reactions / Inés Monte Pérez ; Gutachter: Kallol Ray, Christian Limberg." Berlin : Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://d-nb.info/1129750671/34.
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Allen, John. "Theoretical atomic collision studies : electron transfer to doubly charged carbon ions and the exitation of the lithium atoms by slow hydrogen impact." Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386730.
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Benmeuraiem, Larbi. "Extension de la méthode du potentiel-modèle aux systèmes diatomiques à deux électrons actifs : application au transfert de charge dans les systèmes Ar+6/He, Ar+8/He et C+3/H." Bordeaux 1, 1987. http://www.theses.fr/1987BOR10619.
Abstract:
Extension de la methode du potentiel modele pour la determination des energies electroniques adiatiques de tels systemes. Application a des collisions d'echange de charge aux basses energies (1-1000 ev/uma); accord tres satisfaisant avec l'experience. Pour le systeme c**(3+)/h, ou l'echange de charge s'effectue par un croisement evite aux tres grandes distances internucleaires, observation d'effets de translation importants meme aux basses energies
31
Meng, Yao. "Hydrogen electrochemistry in room temperature ionic liquids." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:be24c6ea-c351-4855-ad9c-98e747ac87e4.
Abstract:
This thesis primarily focuses on the electrochemical properties of the H2/H+ redox couple, at various metallic electrodes in room temperature ionic liquids. Initially, a comprehensive overview of room temperature ionic liquids, RTILs, compared to conventional organic solvents is presented which identifies their favourable properties and applications, followed by a second chapter describing the basic theory of electrochemistry. A third chapter presents the general experimental reagents, instruments and measurements used in this thesis. The results presented in this thesis are summarized in six further chapters and shown as follows. (1) Hydrogenolysis, hydrogen loaded palladium electrodes by electrolysis of H[NTf2] in a RTIL [C2mim][NTf2]. (2) Palladium nanoparticle-modified carbon nanotubes for electrochemical hydrogenolysis in RTILs. (3) Electrochemistry of hydrogen in the RTIL [C2mim][NTf2]: dissolved hydrogen lubricates diffusional transport. (4) The hydrogen evolution reaction in a room temperature ionic liquid: mechanism and electrocatalyst trends. (5) The formal potentials and electrode kinetics of the proton_hydrogen couple in various room temperature ionic liquids. (6) The electroreduction of benzoic acid: voltammetric observation of adsorbed hydrogen at a Platinum microelectrode in room temperature ionic liquids. The first two studies show electrochemically formed adsorbed H atoms at a metallic Pt or Pd surface can be used for clean, efficient, safe electrochemical hydrogenolysis of organic compounds in RTIL media. The next study shows the physicochemical changes of RTIL properties, arising from dissolved hydrogen gas. The last three studies looked at the electrochemical properties of H2/H+ redox couple at various metallic electrodes over a range of RTILs vs a stable Ag/Ag+ reference couple, using H[NTf2] and benzoic acid as proton sources. The kinetic and thermodynamic mechanisms of some reactions or processes are the same in RTILs as in conventional organic or aqueous solvents, but other remarkably different behaviours are presented. Most importantly significant constants are seen for platinum, gold and molybdenum electrodes in term of the mechanism of proton reduction to form hydrogen.
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Gargaud, Muriel. "Transfert de charge entre ions multichargés et hydrogène atomique (et moléculaire) aux basses énergies (thermiques jusqu'à quelques KeV/nucléon) : aspects théoriques." Bordeaux 1, 1987. http://www.theses.fr/1987BOR10550.
Abstract:
Etude theorique de ces collisions dans le domaine des basses energies ou le modele moleculaire permet de decrire les processus de capture electronique conduisant a l'echange de charge, avec une base diabatique issue d'une base adiabatique modifiee par l'introduction de coordonnees de reaction appropriees pour tenir compte du transfert de l'electron au cours de la collision. Illustration par les resultats obtenus avec des ions si**(2+), n**(3+), al**(3+), c**(4+), o**(4+), si**(4+), ti**(4+), n**(5+), o**(5+)
33
Plesniak, Mateusz. "Samarium(II) mediated radical cascades of keto esters for the generation of molecular complexity." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/samariumii-mediated-radical-cascades-of-keto-esters-for-the-generation-of-molecular-complexity(4186c4ea-818c-442c-89cf-61d088174ba4).html.
Abstract:
A highly regio- and diastereoselective approach towards complex 6-membered lactones was developed using allyl/propargyl benzyl ethers and delta keto esters. Crucially, the classical ET reagent SmI2 gave unsatisfactory results and it was necessary to develop and screen new Sm(II) cyclopentadienyl complexes to deliver high selectivity in the transformation. The methodology was extended to a one-pot approach to complex cycloheptanols using SmI2-H2O in a second stage of the process. Samarium(II) folding cascades were developed where simple, linear starting materials are converted to complex polycyclic architectures bearing multiple stereocentres. It was found that, depending on the sidechain in the starting material, it was possible to achieve four different pathways from the common radical intermediate. Crucially, transannular 1,5-HAT from tertiary and benzylic positions was observed to give diverse products. A proposed 1,5-HAT facilitated SmI2-mediated 6-membered lactone radical cyclisations for the first time without an activating proton donor additive. Enantioselective samarium(II) mediated cyclisation cascades were achieved, where simple beta keto esters are converted to complex polycyclic architectures bearing up to five contiguous stereocentres with high diastereo- and enantiocontrol. In the process, a simple and easy to prepare chiral aminodiol was employed which could be recycled after the reaction. Unprecedented, enantioselective transannular radical cascades allowed access to unique 3- dimensional scaffolds inaccessible by other synthetic methods.
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Shaffer, Myron Wayne. "I, evidence of a Quantum Mechanical Tunneling contribution to hydrogen atom transfer reactions of several triplet diaryl carbenes in toluene solution ; II, photochemistry and matrix spectroscopy of 6-azido-4,5,7-trifluoroindole and its implications.. /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487590702990508.
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Attouche, Angie. "Développement de nouvelles réactions radicalaires sans étain en glycochimie : élaboration de spirocétals et débenzylations régiosélectives." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00923135.
Abstract:
Ces travaux de thèse ont consisté à développer de nouvelles réactions radicalaires dans le domaine de la glycochimie. Deux cascades radicalaires, n'utilisant aucun dérivé stannylé et impliquant un transfert d'hydrogène intramoléculaire, ont été étudiées. La première permet de synthétiser des motifs spirocétaliques [6.5] nonanomériques et la deuxième consiste à débenzyler régiosélectivement un éther de benzyle par proximité. Les spirocétals [6.5] nonanomériques sont des motifs présents dans de nombreuses structures de produits naturels. Pour obtenir ce squelette, dont la synthèse est généralement difficile, nous avons développé une cascade radicalaire en chaîne impliquant des précurseurs homopropargyliques et des dérivés phosphorés non toxiques. Plusieurs étapes se succèdent dont l'addition du radical phosphoré sur la triple liaison, un transfert 1,5 d'hydrogène permettant de générer un radical anomère de O-glycoside, à l'origine de la diastéréosélectivité du centre spiranique, et une cyclisation 5-exo-trig. Cette stratégie s'est révélée particulièrement efficace puisque de bons rendements et une excellente diastéréosélectivité ont été obtenus notamment en série glucose et glucosamine. La nouvelle réaction de O-débenzylation par proximité, développée dans la deuxième partie, permet de déprotéger sélectivement un éther de benzyle en α d'un groupement hydroxyle préalablement fonctionnalisé sous forme d'éther de silyle xanthate. Cette réaction se déroule en deux étapes successives dans le même ballon. La première est une cascade radicalaire constituée, entre autres, d'un transfert 1,7 d'hydrogène et de l'addition du radical benzylique, ainsi formé, sur le peroxyde de dilauroyle. L'acétal mixte intermédiaire obtenu est alors hydrolysé lors de la deuxième étape. Cette méthodologie a été appliquée avec succès à divers mono- et disaccharides polybenzylés et s'est révélée efficace en présence de nombreuses autres fonctionnalités chimiques (acétal de benzylidène, azido..).
36
Norberg, Daniel. "Quantum Chemical Studies of Radical Cation Rearrangement, Radical Carbonylation, and Homolytic Substitution Reactions." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8178.
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Carmo, dos Santos Nadia A. "Syntheses and application of nitrogen based polydentate ligand complexes." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3427281.
Abstract:
This Ph.D. thesis describes the versatility of metal complexes with tris(2-pyridylmethyl)amine (TPMA) based ligands to be used either as self-assembling molecular scaffolds with application on molecular recognition and chiroptical probing, or as active catalysts in atom transfer radical polymerization and hydrogen evolving catalysis reactions. Quantitative chirality determination is fundamental due to the broad effect that stereochemistry has in many different scientific fields. Within this subject, there is a strong urge to develop fast and effective methods to perform stereochemical analysis to couple with high throughput screening methods for production or analysis of biological samples. Chiroptical methods are able to provide the speed and accuracy that enantiomeric excess determination measurement needs. Within that scope, three molecular probes for amino acids have been developed allowing to perform enantiomeric determination and absolute configuration by measuring the induced circular dichroism (CD), vibrational circular dichroism (VDC) or circularly polarized luminescence (CPL). The reported systems were able to provide reliable information about the chirality of the studied analytes.
In this dissertation the mechanistic investigation for the elucidation of the self-assembly process of TPMA with amino acids and metals is described. The complex equilibrium that yields the dimeric supramolecular architectures responsible for the chiroptical signals is exposed. The main factor that affects the final products of the reaction as well. Then the effects on the chiroptical response when changing the metal ions on the main structure are reported. Some impressive results were obtained by using Co (II) instead of Zn (II) on the VCD measurements. It was actually possible to enhance the signal intensity by two orders of magnitude. Furthermore, after modifying the initial ligand structure to add a quinolinic moiety in order to give fluorescent properties to the system, it was possible to obtain CPL bands.
Moreover, the versatility of the studied ligands was assessed in other areas like catalysis. Eight novel copper complexes were synthesized and applied as active catalysts in atom transfer radical polymerization (ATRP). Hidroxyquinolinic based cobalt, nickel and iron complexes were evaluated as potential catalysts for hydrogen evolving reactions with positive results.Questa tesi di dottorato descrive la versatilità dei complessi metallici con leganti tris(2-piridilmetil)amminici (TPMA) da utilizzare come scaffold molecolari autoassemblanti con applicazione sul riconoscimento molecolare e sonde chiroptiche, o come catalizzatori attivi nella polimerizzazione radicale a trasferimento atomico e reazioni di catalisi di sviluppo di idrogeno. La determinazione quantitativa della chiralità è fondamentale a causa dell'ampio effetto che la stereochimica ha in molti campi scientifici diversi. All'interno di quest’area, esiste una grande necessità di sviluppare metodi rapidi ed efficaci per eseguire analisi stereochimiche da abbinare a metodi di screening ad alto rendimento per la produzione o l'analisi di campioni biologici. I metodi chiropici sono in grado di fornire la velocità e la precisione necessarie per la determinazione dell’eccesso enantiomerico. Con questo obiettivo sono state sviluppate tre sonde molecolari per amminoacidi che consentono di eseguire la determinazione enantiomerica e la configurazione assoluta misurando il dicroismo circolare indotto (CD), il dicroismo circolare vibrazionale (VDC) o la luminescenza circolare polarizzata (CPL). I sistemi riportati sono stati in grado di fornire informazioni affidabili sulla chiralità degli analiti studiati. In questa dissertazione viene descritta l'indagine meccanicistica per la delucidazione del processo di auto-assemblaggio di TPMA con amminoacidi e metalli. Viene esposto il complesso equilibrio che produce le architetture supramolecolari dimeriche responsabili dei segnali chiropici. Il fattore principale che influisce anche sui prodotti finali della reazione. Quindi vengono riportati gli effetti sulla risposta chiropica al cambiare degli ioni metallici sulla struttura principale. Alcuni risultati significativi sono stati ottenuti utilizzando Co (II) invece di Zn (II) sulle misurazioni VCD. In realtà è stato possibile aumentare l'intensità del segnale di due ordini di grandezza. Inoltre, dopo aver modificare la struttura del legante iniziale per aggiungere un gruppo chinolinico al fine di conferire proprietà fluorescenti al sistema, è stato possibile ottenere le bande CPL. In aggiunta, la versatilità dei leganti studiati è stata valutata in altre aree come la catalisi. Otto nuovi complessi di rame sono stati sintetizzati e applicati come catalizzatori attivi nella polimerizzazione radicale a trasferimento atomico (ATRP). I complessi cobalto, nichel e ferro idrossichinolinici sono stati valutati come potenziali catalizzatori per reazioni di sviluppo di idrogeno con risultati positivi.
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Estes, Deven Paul. "Transition Metal Hydrides that Mediate Catalytic Hydrogen Atom Transfers." Thesis, 2014. https://doi.org/10.7916/D8SF2TDQ.
Abstract:
Radical cyclizations are important reactions in organic chemistry. However, they are seldom used industrially due to their reliance on neurotoxic trialkyltin hydride. Many substitutes for tin hydrides have been developed but none have provided a general solution to the problem.
Transition metal hydrides with weak M-H bonds can generate carbon centered radicals by hydrogen atom transfer (HAT) to olefins. This metal to olefin hydrogen atom transfer (MOHAT) reaction has been postulated as the initial step in many hydrogenation and hydroformylation reactions. The Norton group has shown MOHAT can mediate radical cyclizations of ɑ,ω dienes to form five and six membered rings. The reaction can be done catalytically if 1) the product metalloradical reacts with hydrogen gas to reform the hydride and 2) the hydride can perform MOHAT reactions. The Norton group has shown that both CpCr(CO)₃H and Co(dmgBF₂)₂(H₂O)₂ can catalyze radical cyclizations. However, both have significant draw backs.
In an effort to improve the catalytic efficiency of these reactions we have studied several potential catalyst candidates to test their viability as radical cyclization catalysts. I investigate the hydride CpFe(CO)₂H (FpH). FpH has been shown to transfer hydrogen atoms to dienes and styrenes. I measured the Fe-H bond dissociation free energy (BDFE) to be 63 kcal/mol (much higher than previously thought) and showed that this hydride is not a good candidate for catalytic radical cyclizations.
I have investigated the dynamics of Co(dmgBF₂)₂(H₂O)₂ under hydrogen gas to attempt to observe its hypothesized cobalt hydride. Under large pressures up to 70 atm we see two species one which we assign as the cobalt hydride and one which we assign as a ligand protonated Co(I) complex. These are supported by high pressure NMR studies of the same complexes. By varying the H₂ pressure, we can calculate the hydrogen atom donor ability of the mixture formed under H₂ as 50 kcal/mol. This makes this mixture a very good H• donor.
The Norton group has shown that vanadium hydrides have very weak V-H bonds that donate H* rapidly. However, they cannot be made catalytic under hydrogen gas. I have attempted to regenerate these vanadium hydrides by a sequential reduction then protonation of the metalloradical. With HV(CO)₄dppe this only produced hydrogen gas, presumably by one electron reduction of HV(CO)₄dppe. However, with HV(CO)₄dppf this does not readily occur and this hydride could potentially be a catalyst for radical cyclizations.
Many radical cyclizations involve vinyl (sp²) radicals. I have shown that both the CpCr(CO)₃H and the Co(dmgBF₂)₂(H₂O)₂ systems can catalytically perform metal to alkyne hydrogen atom transfers (MAHAT's) and that these reactions can be used to perform radical cyclizations very efficiently.
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Harvey, Erica Lyn. "Photochemical hydrogen atom transfer reactions of binuclear platinum complexes." Thesis, 1990. https://thesis.library.caltech.edu/2551/1/Harvey_el_1990.pdf.
Abstract:
This thesis focuses on hydrogen atom (H-atom) transfer reactions of the lowest electronic excited state of the d8 dimer [Pt2(P2O5H2)4]4- (the ground state is abbreviated Pt2]; the lowest excited state is a long-lived triplet, abbreviated 3Pt2*). Factors that influence initial rates of reaction of the excited state with alcohol and hydrocarbon H-atom donors are examined in Chapter 2. Observation of a large kinetic deuterium isotope effect (kH/kD=4) for phosphorescence quenching by [alpha]-secphenethyl alcohol verifies the importance of bond strength in determining reaction rates. A plot of H-atom abstraction rates versus C-H bond strengths reveals that bond strength is not the sole determinant of abstraction rate, however. Faster rates are observed when an [alpha]-hydroxy functionality is present, and the size of the substrate also influences abstraction rates. Chapter 3 features characterization of a diplatinum dihydride complex (Pt2H2) that acts as a key intermediate in H-atom transfer reactions. 3Pt2* reacts with hydrogen-atom donors to give a complex characterized by strong absorption at 314 nm; NMR (1H and 31P) and IR spectroscopic studies show that the complex is an axial dihydride (Pt2H2). Reactions of Pt2H2 include photochemical release of H2, rapid thermal reduction of O2, and thermal reduction of HCl to H2. Chapter 4 describes synthesis and characterization of a derivative of Pt2 modified by substitution of electron-withdrawing BF2+ groups for ligand H+. The new compound exhibits photophysical properties (phosphorescence lifetime, quantum yield, absorption and emission maxima) virtually identical with those of 3Pt2*, but dramatically shifted ground-state electrochemical properties (peak potential for oxidation shifted +750 mV). Comparisons of thermal reactivity (preparation of axial dihalide and dihydride complexes) and photochemical reactivity (reductive quenching and H-atom transfer quenching) of the two platinum dimers, detailed in Chapter 5, provide further insight into the factors influencing H-atom transfer in binuclear d8-d8 compounds.
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Sweeney, Robert Joseph. "Hydrogen-Atom Transfer Photochemistry of Tetrakis(µ-pyrophosphito)diplatinate(II)." Thesis, 1990. https://thesis.library.caltech.edu/8545/1/Sweeney_rj_1990.pdf.
Abstract:
In many senses, the hydrogen-atom transfer reactions observed with the triplet excited state of pyrophosphito-bridged platinum(II) dimers resemble the reactions of organic ketone nπ* states. The first two chapters describe our attempts to understand the reactivity differences between these two chromophores. Reactivity of the metal dimers is strongly regulated by the detailed nature of the ligands that ring the axial site, the hydrogen-abstraction center. A hydrogen-bonded network linking the ligands facilitates H-atom transfer quenching with alcohols through the formation of a hydrogen-bonded complex between the alcohol and a dimer. For substrates of equal C-H bond strength that lack a hydroxyl group (e.g., benzyl hydrocarbons), the quenching rate is several orders of magnitude slower.
The shape and size of the axial site, as determined by the ligands, also discriminate among quenchers by their steric characteristics. Very small quenchers quench slowly because of high entropies of activation, while very large ones have large enthalpic barriers. The two effects find a balance with quenchers of "just the right size."
The third chapter discusses the design of a mass spectrometer that uses positron annihilation to ionize neutral molecules. The mass spectrometer creates positron-molecule adducts whose annihilation produces fragmentation products that may yield information on the bonding of positrons in such complexes.
41
D'ALFONSO, CLAUDIO. "Study of the Reactivity of N-oxyl Radicals in Hydrogen Atom Transfer and Electron Transfer Processes." Doctoral thesis, 2012. http://hdl.handle.net/11573/918007.
42
Tsao, Lin, and 曹琳. "Intense field dynamic of hydrogen atom—Fourier-Floquet analysis utilizing the synchrosqueezing transform." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/3t53vd.
Abstract:
碩士國立交通大學
物理研究所
105
Time frequency representation is a useful technique commonly utilized in diverseelds of science and technology despite the diculty of the time-frequency uncertainty. Recently a method called the synchrosqueezing transformation has been proposed to achieve high resolution both in time and frequency. We use this method to analyze the transition amplitude obtained by solving the Schrodinger equation numerically. We take the highly nonlinear excitation of hydrogen as an example to demonstrate the usefulness of this method. When an intense laser eld (wavelength 800nm) irradiated to atoms, they are ionized through so called the tunneling ionization. Recently it is found that electronically excited states are populated as well as ionic states. This highly nonlinear excitation is understood as the key mechanism in remote lasing, or laser induced rain falling. Despite of its importance, the mechanism of excitation itself is not understood well. The purpose of this thesis is to elucidate the physical mechanism using the synchrosqueezing method. We obtained the time frequency spectra of the transition amplitude on excited states, and analyzed them using the adiabatic/nonadiabatic Floquet theory. The dynamics of the hydrogen excitation by intense laser eld is revealed as follows. As the laser is turned on, the wavefunction propagates along the adiabatic Floquet state that is smoothly connected with the initial eigen state (called the initial Floquet state). As the intensity increases, the initial Floquet state is splitted into many photon components. Around the laser peak the initial Floquet state crosses with one of the Floquet states that are smoothly connected to n = 3 eigen states (called the (n = 3)- Floquet state). An even (odd) l eigen state are populated as an even (odd) photon component in the (n = 3)-Floquet state. Nonadiabatic transition from the (n=3)-Floquet state to the Floquet state. converging to the nal eigen state determined the transition probability. An Even (odd) l state has large transition probability when the eigen energy is close to the energy of the even (odd) photon component of the (n = 3)-Floquet state.
43
Li, Gang. "Transition-Metal Complexes Catalyzed Hydrogen Atom Transfer: Kinetic Study and Applications to Radical Cyclizations." Thesis, 2015. https://doi.org/10.7916/D88S4P7C.
Abstract:
Radical cyclizations have been proven to be extremely important in organic synthesis. However, their reliance on toxic trialkyltin hydrides has precluded their practical applications in pharmaceutical manufacturing. Many tin hydride substitutes have been suggested but none of them are adequate alternates to the traditional tin reagent.
Transition-metal hydrides have been shown to catalyze the hydrogenation and hydroformylation of unsaturated carbon-carbon bonds. Theses reactions begin with a Hydrogen Atom Transfer (HAT) from a metal to an olefin, generating a carbon-centered radical. The cyclization of that radical is an effective route to five- and six-membered rings. The HAT will be fastest if the M–H bond is weak. However, making the reaction catalytic will require that the hydride can be regenerated with H2. HCr(CO)3Cp has proven to be a good catalyst for such cyclizations, but it suffers from air sensitivity. The yield of the cyclization product depends on how the rate of radical cyclization compares with the rates of side reactions (hydrogenation and isomerization), so special substituents on a substrate are best installed to increase the cyclization rate.
In attempting to improve the efficiency of radical cyclization I have studied the effect of substituents on the target double bond on the rate of cyclization. A single phenyl substituent has proven to stabilize a radical better than two phenyls. This stabilization leads to faster cyclizations and a higher cyclization yield.
I also have found that Co(dmgBF2)L2 (L = THF, H2O, MeOH…) under H2 is an effective hydrogen atom donor. I have monitored by NMR the catalysis by the system of the hydrogenation of stable radicals (trityl radical and TEMPO radical) and found the rate-determining step to be the activation of hydrogen gas by CoII. The reactive form of the complex is five-coordinated cobalt complex Co(dmgBF2)2L.
The Co/H2 system can also transfer hydrogen atom to C=C bonds, thus initiate radical cyclizations. The resting state of the cobalt is the CoII metalloradical, so a cycloisomerization is obtained. Such a reaction neither loses nor adds any atom and has 100% atom economy.
44
Lin, Fang-Ju, and 林芳如. "Polymers Synthesized by Atom Transfer Radical Polymerization (ATRP) and Their Corresponding Study on Hydrogen Bonded." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/92635484582636528345.
Abstract:
碩士國立交通大學
應用化學系所
93
Since it was discovered in 1995, atom transfer radical polymerization (ATRP) is a rapidly developing area. ATRP is a versatile tool to yield various materials, which are applied in many aspects, such as coatings, adhesives, lubricants, detergents, etc. with low polydispersity and controlled molecular weight. In the physical property of the polymer researches, it is of interest to study the miscibility and specific interaction. In this thesis, the experimental work was divided into three parts: (1) The studies of miscibility behavior and interactions of blends and diblock copolymers. Block copolymers composed of segments with different properties have been of considerable interest. We synthesized Poly(hydroxyethyl methacrylate)-b-Poly(vinylpyrroli- done) (PHEMA-b-PVP) by ATRP and conventional radical polymerization. The interactions in PHEMA-b-PVP diblock copolymers and PHEMA/PVP blends are observed by DSC, FT-IR and high-resolution solid-state 13C NMR spectroscopy. (2) The studies of miscibility behavior and interactions of linear and four-arm blends. Star polymers have different hydrodynamic properties and higher degrees of chain end functionality compared to linear polymers of similar composition. We synthesized the linear and four-arm Poly(tert-butyl acrylate) (PtBA) by ATRP and made them mix with benzoxazine (BZZ). Then, we heated them to yield thmosetting polymer blends. The interactions in linear and four-arm PtBA/PBZZ blends are observed by DSC, FT-IR and high-resolution solid-state 13C NMR spectroscopy. (3) The studies of the influence of specific interactions of POSS-containing polymer blends. By adding inorganic materials into organic polymers, mechanical, thermal, electrical, and magnetic properties are changed from those of pure organic polymers. We synthesized the inorganic-organic polymer hybrids involving POSS compounds by ATRP. The interactions in Poly(methyl methacrylate) (PMMA) and POSS- PMMA/phenolic blends are observed by DSC, FT-IR and 2D IR.
45
Athokpam, Bijyalaxmi. "Theoretical Investigation of H-Bonded O-H Vibrations, H-Atom Transfer and C-H Vibrations via Empirical Valence Bond and Local Mode Based Models." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4211.
Abstract:
In this thesis, I have presented my work on properties of hydrogen(H) bonded systems, H-atom transfer reaction in solution and molecular vibrational spectra through theoretical inves-tigations. The studies are based on two simple models namely, the Empirical Valence Bond (EVB) model and the local-mode based description of vibrations. Chapter 1 is an introduc-tion to these theoretical models. I also briefly introduce the systems investigated along with the model used. Using a EVB based approach, H-bonded O-H vibrations and H atom abstrac-tion reaction by CN radical from ethanol in solution are studied, while a local mode based approach is used for analysing the gas-phase C-H stretch infra-red spectrum of napthalene. A brief description of the contents of the following chapters is presented below.
In Chapter 2, I present our work on the quantum effect of H-motion on H-bonding properties. An EVB based model based on a symmetric O-H···O type of H-bonded system is used for the study. Here I discuss the details of the two-diabatic state model used and the subsequent quantization along one dimensional H-atom motion which is parametric in the donor-acceptor distance. The vibrational states so obtained from the quantization are used to analyse various H-bonding properties such as bond-length, frequency shift and isotope effect. An analysis of the secondary geometric isotope effect (SGIE) using an extension of the two-state model is also presented. The role of bending motion on the H-bond properties are also discussed.
Chapter 3 of the thesis presents our work where we have analysed the correlation of H-bond strength with isotopic fractionation based on the same two-state model. The relative contribution of O-H stretch and bend vibrations, tunneling splitting and SGIE are considered in the analysis.
In Chapter 4 I present our work on the intensity variation associated with O-H stretch vibration involved in a O-H···O type of H-bonded system. Extending the model from Chapter 2 with a Mecke function-based dipole moment the transition intensity is computed. An anal-ysis of variation in fundamental and overtone intensities with H-bond strength and isotope effect (including SGIE) on fundamental intensity are discussed. A study of the trend of these transition intensities due to variation of Mecke parameters of the dipole moment function is also discussed in this chapter.
Chapter 5 discusses our work on H-atom abstraction reaction of the CN radical with ethanol in solution based on an EVB model approach coupled with molecular dynamics simulations. A two-state EVB model is used to define the reaction system and the details of the reaction-system models are described. The reaction system in solvated H2O and CHCl3 and the dynamics of the H-abstraction are analysed in terms of the energy profile and post-transition state energetics. An analysis of solvent involvement in the processes for the two solvents are also presented.
Our study on the C-H stretch infrared region of Napthalene employing a local-mode normal-model based approach is presented in Chapter 6. Using a curvilinear coordinate framework to set up the vibrational Hamiltonian, the calculated spectra is presented. The details of this Hamiltonian and the use of its eigenstates to describe the coupled states that make up the spectral bands are presented in this chapter.
Chapter 7 briefly summarize the works undertaken and highlight the important results obtained from our studies.
46
Ciąćka, Piotr. "Ultrafast dynamics of intramolecular proton transfer." Doctoral thesis, 2016. https://depotuw.ceon.pl/handle/item/1940.
Abstract:
The following work describes studies of proton or hydrogen transfer, one of the most
basic molecular processes. Employing suitable model molecules in the form of porphycene
and its derivatives as well as advanced ultrafast optical experimental methods,
insight into hydrogen dynamics is o ered with femtosecond temporal resolution in both
ground and excited state without the requirement for spectral changes between the transfer
process substrates and products, a combination of features unavailable in other techniques.
In the course of the studies, a custom experimental setup was built with improved
sensitivity and exibility over the pioneer of the technique. e construction and characterization
of the apparatus as well as the work ow of obtaining hydrogen transfer rates
are described. e setup was employed to study a large number of porphycene derivatives
allowing, together with other experimental and computational methods, the elucidation
of hydrogen transfer rate-a ecting factors. Next, hydrogen tunnelling as a transfer mechanism
in porphycene was investigated, with results revealing multiple tunnelling modes,
including vibrationally-enhanced tunnelling signi cant even at room temperature. Vibrational
degrees of freedom were also the focus of coherent control experiments aimed
at in uencing the outcome of various molecular processes in porphycenes using shaped
laser pulses. Experimental realization of several useful pulse shapes is presented, as is
their application to control of excited state populations and attempts to in uence hydrogen
transfer rates.Niniejsza praca przedstawia badania nad jednym z najbardziej fundamentalnych procesów molekularnych, zjawiskiem przeniesienia protonu (atomu wodoru). Użyteczne modelowe molekuły, por cyna i jej pochodne, oraz zaawansowane ultraszybkie metody optyczne umożliwiły obserwację dynamiki protonów z femtosekundową rozdzielczością czasową, w stanie podstawowym i wzbudzonym, nawet przy braku zmian spektralnych odróżniających produkty od substratów procesu. W trakcie badań zbudowano układ doświadczalny o zwiększonej czułości i poszerzonym zakresie stosowalności w porównaniu z poprzednimi, pionierskimi studiami. Opisano konstrukcję i charakteryzację parametrów układu oraz sposób przeprowadzania eksperymentów i uzyskiwania stałych szybkości przeniesienia atomu wodoru. Układ został użyty w pomiarach kinetyk przeniesienia atomu wodoru w dużej liczbie pochodnych por cyn, co przy wsparciu innych technik doświadczalnych i obliczeniowych pozwoliło wyróżnić czynniki wpływające na dynamikę procesu. W dalszej kolejności przebadano tunelowanie jako mechanizm przeniesienia atomu wodoru. Wyniki uwidoczniły kilka kanałów reakcji wykorzystujących efekt tunelowy, w tym tunelowanie wspomagane wibracyjnie, które wnosi istotny wkład do procesu nawet w temperaturze pokojowej. Wibracyjne stopnie swobody stały również u podstaw badań z dziedziny kontroli koherentnej. Ich celem było wpływanie na przebieg procesów molekularnych w por - cynie przy pomocy kształtowanych impulsów laserowych. Przedstawiono eksperymentalną realizację różnych kształtów impulsów oraz ich zastosowanie w kontroli populacji stanu wzbudzonego oraz w próbach kontroli szybkości przeniesienia atomu wodoru.
47
Devendra, Mani *. "Microwave Spectroscopic and Atoms in Molecules Theoretical Investigations on Weakly Bound Complexes : From Hydrogen Bond to 'Carbon Bond'." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3465.
Abstract:
Weak intermolecular interactions have very strong impact on the structures and properties of life giving molecules like H2O, DNA, RNA etc. These interactions are responsible for many biological phenomena. The directional preference of some of these interactions is used for designing different synthetic approaches in the supramolecular chemistry. The work reported in this Thesis comprises of investigations of weak intermolecular interactions in gas phase using home-built Pulsed Nozzle Fourier Transform Microwave (PN-FTMW) spectrometer as an experimental tool and ab-initio and Atoms in Molecules (AIM) theory as theoretical tools. The spectrometer which is coupled with a pulsed nozzle is used to record pure rotational spectra of the molecular clusters in a jet cooled molecular beam. In the molecular beam molecules/complexes are free from interactions with other molecules/complexes and thus, spectroscopy in the molecular beams provides information about the 'isolated' molecule/complex under investigation. The rotational spectra of the molecules/complexes in the molecular beam provide their geometry in the ground vibrational states. These experimental geometries can be used to test the performance and accuracy of theoretical models like ab-initio theory, when applied to the weakly bound complexes. Further the AIM theory can be used to gain insights into the nature and strength of the intermolecular interactions present in the system under investigation. Chapter I of this Thesis gives a brief introduction of intermolecular interactions. Other than hydrogen bonding, which is considered as the most important intermolecular interaction, many other intermolecular interactions involving different atoms have been observed in past few decades. The chapter summarizes all these interactions. The chapter also gives a brief introduction to the experimental and theoretical methods used to probe these interactions. In Chapter II, the experimental and theoretical methods used in this work are summarized. Details of our home-built PN-FTMW spectrometer are given in this chapter. The chapter also discusses briefly the theoretical methods like ab-initio, AIM and Natural bond orbital (NBO) analysis. We have made few changes in the mode of control of one of our delay generators which have also been described.
Chapter III and Chapter V of this Thesis are dedicated to the propargyl alcohol complexes. Propargyl alcohol (PA) is a molecule of astrophysical interest. It is also important in combustion chemistry since propargyl radical is considered as the precursor in soot formation. Moreover, PA is a multifunctional molecule, having a hydroxyl (-OH) and an acetylenic (-C≡C-H) group. Both of the groups can individually act as hydrogen bond acceptor as well as donor and thus PA provides an exciting possibility of studying many different types of weak interactions. Due to internal motion of -OH group, PA monomer can exist in gauche as well as trans form. However, rotational spectra of PA-monomer show the presence of only gauche conformer. In Chapter III, rotational spectra of Ar•••PA complex are discussed. The pure rotational spectra of the parent Ar•••PA complex and its two deuterated isotopologues, Ar•••PA-D (OD species) and Ar•••PA-D (CD species), could be observed and fitted within experimental uncertainty. The structural fitting confirmed a structure in which PA is present as gauche conformer and argon interacts with both the O-H group and the acetylenic group leading to Ar•••H-O and Ar•••π interactions respectively. Presence of these interactions was further confirmed by AIM theoretical analysis. In all the three isotopologues c-type rotational transitions showed significant splitting. Splitting patterns in the three isotopologues suggest that it originates mainly due to the large amplitude motion of the hydroxyl group and the motion is weakly coupled with the carbon chain bending motion. No evidence for the complex with trans conformer of PA was found. Although, we could not observe Ar•••trans-PA complex experimentally, we decided to perform ab-initio and AIM theoretical calculations on this complex as well. AIM calculations suggested the presence of Ar•••H-O and a unique Ar•••C interaction in this complex which was later found to be present in the Ar•••methanol complex as well. This prompted us to explore different possible interactions in methanol, other than the well known O-H•••O hydrogen bonding interactions, and eventually led us to an interesting interaction which we termed as carbon bond. Chapter IV discusses carbon bonding interaction in different complexes. Electrostatic potential (ESP) calculations show that tetrahedral face of methane is electron-rich and thus can act as hydrogen/halogen bond acceptor. This has already been observed in many complexes, e.g. CH4•••H2O/HF/HCl/ClF etc., both experimentally and theoretically. However, substitution of one of the hydrogens of methane with -OH leads to complete reversal of the properties of the CH3 tetrahedral face and this face in methanol is electron-deficient. We found that CH3 face in methanol interacts with electron rich sites of HnY molecules and leads to the formation of complexes stabilized by Y•••C-X interactions. This interaction was also found to be present in the complexes of many different CH3X (X=OH/F/Cl/Br/NO2/NF2 etc.) molecules. AIM, NBO and C-X frequency shift analyses suggest that this interaction could be termed as "carbon bond". The carbon bonding interactions could be important in understanding hydrophobic interactions and thus could play an important role in biological phenomena like protein folding. The carbon bonding interaction could also play a significant role in the stabilization of the transition state in SN2 reactions. In Chapter V of this Thesis rotational spectra of propargyl alcohol dimer are discussed. Rotational spectra of the parent dimer and its three deuterated (O-D) isotopologues (two mono-substituted and one bi-substituted) could be recorded and fitted within experimental uncertainty. The fitted rotational constants are close to one of the ab-initio predicted structure. In the dimer also propargyl alcohol exists in the gauche form. Atoms in molecules analysis suggests that the experimentally observed dimer is bound by O-H•••O, O-H•••π and C-H•••π interactions. Chapter VI of the thesis explores the 'electrophore concept'. To observe the rotational spectra of any species and determine its rotational constant by microwave spectroscopy, the species should have a permanent dipole moment. Can we obtain rotational constants of a species having no dipole moment via microwave spectroscopy? Electrophore concept can be used for this purpose. An electrophore is an atom or molecule which could combine with another molecule having no dipole moment thereby forming a complex with a dipole moment, e.g. Argon atom is an electrophore in Ar•••C6H6 complex. The microwave spectra of Ar•••13CC5H6 and Ar•••C6H5D complexes were recorded and fitted. The A rotational constant of these complexes was found to be equal to the C rotational constant of 13CC5H6 and C6H5D molecules respectively and thus we could determine the C rotational constant of microwave 'inactive' 13CC5H6. This concept could be used to obtain the rotational spectra of parallel displaced benzene-dimer if it exists.
We recently showed that the square pyramidal Fe(CO)5 can act as hydrogen bond acceptor. Appendix I summarizes the extension of this work and discusses interactions of trigonal bipyramidal Fe(CO)5 with HF, HCl, HBr and ClF. Our initial attempts on generating a chirped pulse to be used in a new broadband spectrometer are summarized in Appendix II. Preliminary investigations on the propargyl•••water complex are summarized in Appendix III.
48
Devendra, Mani *. "Microwave Spectroscopic and Atoms in Molecules Theoretical Investigations on Weakly Bound Complexes : From Hydrogen Bond to 'Carbon Bond'." Thesis, 2013. http://etd.iisc.ernet.in/2005/3465.
Abstract:
Weak intermolecular interactions have very strong impact on the structures and properties of life giving molecules like H2O, DNA, RNA etc. These interactions are responsible for many biological phenomena. The directional preference of some of these interactions is used for designing different synthetic approaches in the supramolecular chemistry. The work reported in this Thesis comprises of investigations of weak intermolecular interactions in gas phase using home-built Pulsed Nozzle Fourier Transform Microwave (PN-FTMW) spectrometer as an experimental tool and ab-initio and Atoms in Molecules (AIM) theory as theoretical tools. The spectrometer which is coupled with a pulsed nozzle is used to record pure rotational spectra of the molecular clusters in a jet cooled molecular beam. In the molecular beam molecules/complexes are free from interactions with other molecules/complexes and thus, spectroscopy in the molecular beams provides information about the 'isolated' molecule/complex under investigation. The rotational spectra of the molecules/complexes in the molecular beam provide their geometry in the ground vibrational states. These experimental geometries can be used to test the performance and accuracy of theoretical models like ab-initio theory, when applied to the weakly bound complexes. Further the AIM theory can be used to gain insights into the nature and strength of the intermolecular interactions present in the system under investigation. Chapter I of this Thesis gives a brief introduction of intermolecular interactions. Other than hydrogen bonding, which is considered as the most important intermolecular interaction, many other intermolecular interactions involving different atoms have been observed in past few decades. The chapter summarizes all these interactions. The chapter also gives a brief introduction to the experimental and theoretical methods used to probe these interactions. In Chapter II, the experimental and theoretical methods used in this work are summarized. Details of our home-built PN-FTMW spectrometer are given in this chapter. The chapter also discusses briefly the theoretical methods like ab-initio, AIM and Natural bond orbital (NBO) analysis. We have made few changes in the mode of control of one of our delay generators which have also been described.
Chapter III and Chapter V of this Thesis are dedicated to the propargyl alcohol complexes. Propargyl alcohol (PA) is a molecule of astrophysical interest. It is also important in combustion chemistry since propargyl radical is considered as the precursor in soot formation. Moreover, PA is a multifunctional molecule, having a hydroxyl (-OH) and an acetylenic (-C≡C-H) group. Both of the groups can individually act as hydrogen bond acceptor as well as donor and thus PA provides an exciting possibility of studying many different types of weak interactions. Due to internal motion of -OH group, PA monomer can exist in gauche as well as trans form. However, rotational spectra of PA-monomer show the presence of only gauche conformer. In Chapter III, rotational spectra of Ar•••PA complex are discussed. The pure rotational spectra of the parent Ar•••PA complex and its two deuterated isotopologues, Ar•••PA-D (OD species) and Ar•••PA-D (CD species), could be observed and fitted within experimental uncertainty. The structural fitting confirmed a structure in which PA is present as gauche conformer and argon interacts with both the O-H group and the acetylenic group leading to Ar•••H-O and Ar•••π interactions respectively. Presence of these interactions was further confirmed by AIM theoretical analysis. In all the three isotopologues c-type rotational transitions showed significant splitting. Splitting patterns in the three isotopologues suggest that it originates mainly due to the large amplitude motion of the hydroxyl group and the motion is weakly coupled with the carbon chain bending motion. No evidence for the complex with trans conformer of PA was found. Although, we could not observe Ar•••trans-PA complex experimentally, we decided to perform ab-initio and AIM theoretical calculations on this complex as well. AIM calculations suggested the presence of Ar•••H-O and a unique Ar•••C interaction in this complex which was later found to be present in the Ar•••methanol complex as well. This prompted us to explore different possible interactions in methanol, other than the well known O-H•••O hydrogen bonding interactions, and eventually led us to an interesting interaction which we termed as carbon bond. Chapter IV discusses carbon bonding interaction in different complexes. Electrostatic potential (ESP) calculations show that tetrahedral face of methane is electron-rich and thus can act as hydrogen/halogen bond acceptor. This has already been observed in many complexes, e.g. CH4•••H2O/HF/HCl/ClF etc., both experimentally and theoretically. However, substitution of one of the hydrogens of methane with -OH leads to complete reversal of the properties of the CH3 tetrahedral face and this face in methanol is electron-deficient. We found that CH3 face in methanol interacts with electron rich sites of HnY molecules and leads to the formation of complexes stabilized by Y•••C-X interactions. This interaction was also found to be present in the complexes of many different CH3X (X=OH/F/Cl/Br/NO2/NF2 etc.) molecules. AIM, NBO and C-X frequency shift analyses suggest that this interaction could be termed as "carbon bond". The carbon bonding interactions could be important in understanding hydrophobic interactions and thus could play an important role in biological phenomena like protein folding. The carbon bonding interaction could also play a significant role in the stabilization of the transition state in SN2 reactions. In Chapter V of this Thesis rotational spectra of propargyl alcohol dimer are discussed. Rotational spectra of the parent dimer and its three deuterated (O-D) isotopologues (two mono-substituted and one bi-substituted) could be recorded and fitted within experimental uncertainty. The fitted rotational constants are close to one of the ab-initio predicted structure. In the dimer also propargyl alcohol exists in the gauche form. Atoms in molecules analysis suggests that the experimentally observed dimer is bound by O-H•••O, O-H•••π and C-H•••π interactions. Chapter VI of the thesis explores the 'electrophore concept'. To observe the rotational spectra of any species and determine its rotational constant by microwave spectroscopy, the species should have a permanent dipole moment. Can we obtain rotational constants of a species having no dipole moment via microwave spectroscopy? Electrophore concept can be used for this purpose. An electrophore is an atom or molecule which could combine with another molecule having no dipole moment thereby forming a complex with a dipole moment, e.g. Argon atom is an electrophore in Ar•••C6H6 complex. The microwave spectra of Ar•••13CC5H6 and Ar•••C6H5D complexes were recorded and fitted. The A rotational constant of these complexes was found to be equal to the C rotational constant of 13CC5H6 and C6H5D molecules respectively and thus we could determine the C rotational constant of microwave 'inactive' 13CC5H6. This concept could be used to obtain the rotational spectra of parallel displaced benzene-dimer if it exists.
We recently showed that the square pyramidal Fe(CO)5 can act as hydrogen bond acceptor. Appendix I summarizes the extension of this work and discusses interactions of trigonal bipyramidal Fe(CO)5 with HF, HCl, HBr and ClF. Our initial attempts on generating a chirped pulse to be used in a new broadband spectrometer are summarized in Appendix II. Preliminary investigations on the propargyl•••water complex are summarized in Appendix III.