Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236070
Title: Studies on natural Raman optical activity.
Author: Rivero, Juan Ricardo Escribano.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1985
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Abstract:
Optical activity associated with vibrations of chiral molecules can provide much stereochemical information. There are two techniques which observe vibrational optical activity (VOA), namely: infrared circular dichroism (IRCD) and vibrational Raman optical activity (VROA). The first, IRCD, is an extension of circular dichroism into the infrared and measures a difference in absorbance of incident left and right circularly polarized infrared radiation. VROA is concerned with a difference in the intensity of Raman scattering when the chiral system is illuminated with left and right circularly polarized radiation. Recent reviews that cover both techniques are in the references of the Summary. This thesis is divided into two main parts. The first (Chapters 1 to 4) is concerned with theoretical studies of ROA. The second (Chapters 5 to 8) with calculations of the observable parameters in VROA and their comparison with experimental results. Chapter 1 comprises a theoretical study in molecular scattering tensors: one significant new result was the discovery of a Stokes-antiStokes asymmetry in the ROA observables. In Chapter 2 is reviewed the experimental conditions in which VROA experiments have been carried out and how the artifacts will affect their spectra. For this, firstly, it has been necessary to provide a general extension of the established equations which give the ROA observables at any point in space. Subsequently a new and more realistic parameter in ROA is defined in terms of power. The difference with the original one is not important in the experimental conditions in which the spectra are recorded, but it is relevant from the scientific aesthetic point of view. Particular cases are derived from these general equations in total agreement with the original and well established ones. In all cases the influence of artifacts coming from imperfectly modulated right and left circularly polarized incident light has been considered. Chapter 3 is a generalization of the "two group model" in VROA using the bond polarizability theory. The model has been extended to include deformations of non-axially symmetric groups. A general critical revision of these formulae is provided. Chapter 4 is a survey of miscellanea in VROA. An interesting prediction is given in the case of Fermi resonance. At the end of this chapter a new selection rule is proposed in VROA which relates polarized and depolarized VROA spectra. This rule is analogous to that which relates polarized and depolarized conventional Raman spec tr a. The second part of the thesis is devoted to calculations of the observable parameters in VROA and their comparison with the experimental results. The molecule CBrClFH has not yet been studied experimentally but it is a good (Chapter 5) example for calculations because the results can be compared with those from other theories such as the "atom dipole interaction model". Chapter 6 treats another easy chiral molecule, epoxypropane. The advantage of this molecule is that it can be tested with its experimental spectrum and considering the approximate force field we can say that the comparison is good. Chapters 7 and 8 deal with small chiral molecules derived from cyclohexanone, deuterated and methylated. We have included in our calculations two conformers, not just the most stable, and weighting each contributi~n to the total VROA spectrum. The big couplet centered at 500 cm-1 in the (R)-(+)-3-methylcyclohexanone is explained with these considerations. Surprisingly the results do not fit very well in the cases of the deuterated cyclohexanones.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.236070  DOI: Not available
Keywords: Atomic physics & molecular physics
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