Studies in ring-chair ..... group effects

Abstract

The thesis entitled "Studies in Ring-Chain Tautomerism" consists of four chapters and an appendix. A study of the kinetics of alkaline hydrolysis of methyl 3-benzoylpropionate, methyl 4-benzoylbutyrate and methyl 5-benzoylvalerate and their ring-substituted derivatives is described in the first chapter. The influence of geometrical factors on neighbouring keto participation has been examined. It is found that methyl 3-benzoylpropionate undergoes solvolysis by substantial keto participation (I) while methyl 5-benzoylvalerate solvolyses by direct attack of the hydroxide ion on the carbomethoxy function (III). The case of methyl 4-benzoylbutyrate is in between the two. That keto participation is indeed the cause of rate enhancement in benzoylpropionate series is established by determining the dissociation constants of the corresponding acids. Unlike in the case of ester hydrolysis, ring substituents do not wield appreciable influence on the dissociation of these acids. In the second chapter, solvolysis of some unsymmetrical phthalic acid half-ester chlorides has been described. The results point to the fact that the half-ester chlorides do not exist in tautomeric equilibrium, contrary to literature reports. Evidence has been obtained for the intermediacy of the oxonium ion IV in the Friedel-Crafts and related reactions of isomeric half-ester chlorides. The third chapter describes the structure and reactivity of some ?- and ?-keto acid chlorides based on kinetic and spectral data. A critical survey of over one hundred acid chlorides having neighbouring groups has been done based on the present work, work from this laboratory and the information available in the literature. Some useful generalisations have been made. A new synthesis of o-acetonylbenzoic acid from phthalonic acid and a new method of reduction of dithiosalicylic acid to thiosalicylic acid have been described. The kinetics of alcoholysis of substituted o-benzoylbenzoyl chlorides is described in the fourth chapter. Unlike the hydrolysis of pseudo acid chlorides, the mechanism of alcoholysis depends upon the alcohol used. Mostly, alcoholysis proceeds by a bimolecular pathway. The appendix describes an attempted synthesis of 'Dwaita-nhanes'—a new class of compounds containing two aromatic systems—a cyclo or open one (2?) and a benzene (6?). Due to the high strain involved in the formation of these compounds (three-membered rings), they were highly unstable and a thorough study of the two (V & VI) compounds synthesised could not be carried out.