Conformations of some saturated carbonyl compounds. Part II. Infrared spectra of ethyl formate, acetate, propionate, and n-butyrate, and [2H5]ethyl n-butyrate

Abstract

Infrared spectra of ethyl formate, acetate, propionate, and n-butyrate, and [²H₅]ethyl n-butyrate are reported. The effects on these spectra of cooling solutions in carbon disulphide to –100 °C and of solidification are reported and are interpreted in terms of conformational equilibria. Evidence for the presence of one pair of conformers, derived probably from rotation about the O–Et bond, has been found in all the esters examined; an enthalpy difference (ΔH°) of 315 ± 25 cal mol^–1 between high- and low-energy conformers has been obtained for ethyl acetate. Evidence has also been obtained for the presence of an additional equilibrium in ethyl and [²H₅]ethyl n-butyrates associated with rotations within the n-butyl chain.