Enolisation of Simple Carbonyl Compounds and Related Reactions

Abstract

Publisher Summary This chapter focuses on the enolization of simple carbonyl compounds and related reactions. It presents an overview of the data on the tautomerism of simple carbonyl compounds. “Simple” designates compounds are those that lack enol-stabilizing functions accounting for a significant or great amount of enol. The chapter discusses the mechanism of keto-enol tautomerization and presents the results on stereochemical aspects of enolization (or enolate formation) and on regioselectivity when two enolization sites are in competition. Because the keto-enol equilibrium is so displaced toward the keto form that the enol concentration cannot usually be measured as a function of time, the keto–enol tautomerization cannot be studied directly for simple carbonyl compounds. Most kinetic studies have made use of the property that enolization is the rate-limiting stage of some stepwise reactions that have a rate corresponding to enolization or ionization itself. Enolization and ionization are also the first stages of some elimination reactions, such as aldolization and alkylation, but in most cases, the enolization (or ionization) process is not rate-limiting. Thermodynamic data on enol and enolate formation are needed to understand the kinetic behavior of these reactions; a complete picture must include data on the subsequent steps.