Ring–Chain Isomeric Conversions of Aldehydo-carboxylic and Keto-carboxylic Acids and Their Derivatives

Ring–chain isomeric (including tautomeric) conversions of aldehydo- and keto-carboxylic acids and their chlorides, amides, hydrazides, esters, and mixed anhydrides are reviewed. The possibilities of using physical methods (ultraviolet, infrared, and proton magnetic resonance spectroscopy) for the identification and quantitative determination of isomers are discussed. The effect of structural factors on the relative stability of isomers is analysed. Conditions are elicited under which interconversion occurs or equilibrium is observed. A list of 207 references is included.