Studies in ring-chain tautomerism Ph.D. Thesis

Abstract

The thesis entitled “Studies in Ring-Chain Tautomerism” consists of three chapters:

Chapter 1 This chapter presents a brief review of Ring-Chain Tautomerism. The implications of this phenomenon in some biological reactions are discussed briefly. Systematic studies of ring-chain tautomerism of ?- and ?-keto acids, amides, acid chlorides, and esters are included.

Chapter 2 This chapter describes the kinetic study of base-catalyzed hydrolysis of various pseudoesters derived from ?-keto acids. The effect of changes in the electronic environment and the leaving group of the pseudoester on the rate of hydrolysis is discussed. The results favor a concerted cleavage of the lactone ring rather than a stepwise mechanism involving the intermediacy of an alkoxide derivative of the hemiketal (R-C-C-OR?). The overall rate in the B_AC2 alkaline hydrolysis of the esters is determined by the conjugative ability of the leaving group rather than its leaving group ability.

Chapter 3 This chapter discusses the results of alkaline hydrolysis of normal esters of o-benzoylbenzoic acid. Evidence has been presented for the operation of a dual mechanism in some cases. It has been shown that the major factor responsible for the rate enhancement in keto-assisted hydrolysis is the larger rate of attack of hydroxide ion on the ketone compared to that on the ester. The first step, involving the attack of hydroxide ion on the keto carbonyl group forming the tetrahedral intermediate, is the major factor controlling the rate. The consequence of this view-viz., relatively small effect of leaving groups in keto esters as compared to benzoate esters-has been demonstrated in the case of t-butyl o-benzoylbenzoate.