Because polypeptides present a repeating sequence of amide bonds, lactams provide good model compounds for investigating the angular dependencies of coupling constants over a range of rigid conformations. A number of ¹³C labeled lactams were synthesized to cover a range of dihedral angles; experimental and theoretical carbon-carbon and carbon-hydrogen coupling constants were obtained to give the relationships between the vicinal coupling constants ³J[C(O)-N-C-C], ³J[C(O)-N-C-H] and dihedral angle φ. Vicinal ¹³C-¹³C coupling constants for dihedral angles in the range of 90° to 180° were obtained unambiguously from the coupling between the carbonyl and carbons in the side chains of lactams. However, due to coupling via multiple paths, vicinal ¹³C-¹³C coupling constants for dihedral angles ranging from 0° to 90° were estimated by excluding the contributions from the geminal ²J[C(O)-C-C] or vicinal ³J[C(O)-C-C-C] couplings in the lactam rings. The experimental and theoretical results show that the angular dependence of vicinal ¹³C-¹³C coupling constants do not follow a simple Karplus type relationship, especially at small dihedral angles. It was found that geminal ²J[C(O)-N-C] were small ( < 0.3 Hz). However, the ²J[C(O)-N-C] in the cis arrangement are shifted to about 2.2 Hz in N-methyl substituted lactams while in the trans arrangement the values are about 4.4 Hz. Geminal ¹³C-¹³C coupling constants ²J[(C(O)-N-C)] also provide a useful tool in stereochemical studies.

The results obtained by this new method are shown to be able to account for most of the shortcomings of the earlier methods, in particular their failure satisfactorily to explain the quenching of luminescence in cis-polyacetylene and their poor predictions of the relative strengths of the two photoinduced absorption peaks in polythiophene. The ability of trans-polyacetylene (t-PA) to support a novel type of dynamic defect known as a breather is also verified. A quantitative estimate is made of the mobility of the fundamental defect in t-PA, known as a soliton, and this is in good agreement with experiment.

With a large number of carbon-carbon spin-spin coupling constants now determined and the dihedral angle dependence of vicinal coupling constants reported, application of this coupling constants data was attempted to a conformational study.

The correlation between the carbon-proton and proton-proton coupling constants have been studied in various 13 systems. Isocrotonic acid-carboxyl-3C, crotonic acid- 13 13 carboxyl-3C, and 5-norbornene-2-carboxylic acid-carboxyl-3C- 1,5,6,7,7-hexachloro were synthesized and their carbonproton coupling constants were analyzed. Nmr studies showed the magnitudes of the carbon-proton coupling constants to correlate well with analogous protonproton coupling constants, although the values of the couplings were larger than expected. The geminal olefinic couplings were considerably larger than all other couplings, but they were self-consistent. The signs of the carbon-proton coupling constants also were in agreement without exception with the signs of analogous proton-proton coupling constants.

This thesis is a partial investigation of instabilities in the interstellar gas which are driven by a coupling between the ambient radiation field and the gas, and which do not arise when this coupling is missed out. The modes of couplings considered are, firstly, the attenuation of the radiation with the concomitant effects on the temperature, density and composition of the gas, in various combinations. Secondly, velocity dependent effects are examined in various circumstances and thirdly, radiation pressure, not included in the other two, is looked at in the simple case in which temperature and compositional changes are excluded. The explanation of why these instabilities may be of interest, and an outline of the extent to which similar instabilities have been investigated, is given in Chapter 1. Chapter 2 gives details of the basic equations used in the case in which the absorption line shape is ignored. Many of the equations are used in the other chapters. The equations are linearised in perturbations of the density, temperature, radiation field and composition, and the resulting dispersion relationship is found for a harmonic perturbation. Because of the attenuation term in the radiative transfer equation, the polynomial has complex coefficients. In Chapter 3 we investigate the properties of the roots of a complex polynomial by an extension of Routh's methods, and derive a set of criteria to determine the number of roots which have positive real part. These roots correspond to exponentially growing perturbations, or, in other words, they correspond to instabilities. Later in the chapter we apply these methods to Field's dispersion relationship for thermal instabilities and derive many of his conclusions in a fairly simple way. By a slight extension the method yields estimates of the growth times of the instabilities. Some related situations are also examined in a similar way. After the detour of Chapter 3, Chapter 4 gives details of some models of the heating and cooling of the interstellar gas as well as of the reactions to be considered, namely the formation and destruction of H₂ and of carbon ions. Some of the limitations of the models are also discussed and the roots of the dispersion relation are given for different values of the parameters. New instabilities do appear; for H₂ their timescales of growth are rather too long to be of interest; for carbon no short timescale instabilities are discovered. Chapter 5 gives similar details for a system of pure hydrogen gas which may be of interest in studies of the formation of the first generation of stars. In Chapter 6 there is a criticism of an earlier work by Schatzman on a similar subject, in which it is shown that his analysis was wrong. Chapter 7 deals with a new possibility, namely that, as the gas moves, photons will be seen to be shifted in frequency and so the molecules will be exposed to a new set of destructive photons at frequencies which have not been selectively absorbed in the unperturbed gas. First the simplest case, that in which the temperature is unperturbed, is treated analytically. The attenuation of the radiation field is not considered. The effectiveness of this doppler-induced effect depends upon both the absorption profile and the radiation spectrum; these factors as well as temperature perturbations are included next. Both line absorption and continuum absorption are considered. The former is used to investigate the stability of the interstellar gas and of pure hydrogen gas, where hydrogen molecules are dissociated by line absorption; the latter is used in connection with HII regions and also the interstellar gas where the photodissociated species are hydrogen atoms and neutral carbon respectively. Radiation pressure was not included in the previous chapters but in Chapter 8 a modified version of Field's theory of instabilities driven by radiation pressure is presented. The new feature is that the frequency dependence of the absorption coefficient is included in the equations and this, in the case of a flat radiation spectrum, leads to an exact cancellation of the dominant term in Field's equation. Several restrictive features of Field's conclusions are thus modified and seem to make this instability rather more useful in the study of instabilities in the interstellar gas than it appeared in Field's work.

by Wing-keung Mak. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 51-53). / by Wing-keung Mak. / Acknowledgments --- p.i / Abstract --- p.ii / Table of Content --- p.iii / Chapter Chapter One --- Introduction --- p.1 / Chapter Chapter Two --- Theory / Chapter 2.1 --- Theory of Two-wave Coupling --- p.3 / Chapter 2.2 --- Theory of Fanning --- p.8 / Chapter 2.3 --- Theory of Time Dependent Absorption Coefficients of Photorefractive Crystals --- p.10 / Chapter Chapter Three --- Photorefractive Fabry-Perot Etalon / Chapter 3.1 --- Theory and Numerical Computation --- p.12 / Chapter 3.2 --- Summary of Crystal Parameters --- p.15 / Chapter 3.3 --- Experimental Studies of Interference Patterns --- p.16 / Chapter 3.4 --- Intensity Dependence of Fabry-Perot Etalon Interference Patterns --- p.25 / Chapter 3.5 --- Fanning --- p.29 / Chapter 3.6 --- Bright Spots on Interference Patterns --- p.31 / Chapter Chapter Four --- Time Dependent Absorption Coefficients of Photorefractive Crystals / Chapter 4.1 --- Experiments Using Laser Light --- p.34 / Chapter 4.2 --- Experiments Using White Light --- p.44 / Chapter Chapter Five --- Conclusion and Future Outlook --- p.49 / References --- p.51

No description available.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 152-158).

The body of information concerning carbon-carbon spin-spin coupling constants now includes a large number of coupling constants, the establishment of a dihedral angular dependence on 3JCC, and the application of 3JCC to conformational analysis. This study adds another dimension to the growing wealth of information associated with 13 C-NMR: the influence of some non-bonded interactions on 3JCC Four types of non-bonded interactions that could influence vicinal carbon-carbon NMR coupling constants were investigated. To facilitate the NMR studies, a variety of 13C-labeled compounds were synthesized.

A model system to calculate single-path coupling constant was devised to see if the couplings are additive in a system which has a dual-pathway. The system chosen was o-methyl-13C-benzoic acid. Because of anomalies in the data, the series was extended. Hybridization of the label appeared to have relatively little effect, and the conformation of the substituents very important.