Conformations of some saturated carbonyl compounds. Part III. Infrared spectra of isomeric propyl and butyl formates and acetates

Abstract

I.r. spectra of n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, and t-butyl formates and acetates are reported. The effects on these spectra of cooling liquid films and of solidification are interpreted in terms of conformational equilibria. Evidence for the presence of rotational equilibria has been obtained in all the esters except for isopropyl formate, isopropyl, and t-butyl acetate. Conformers are considered to arise from rotation about the HCO–O bond in t-butyl formate (for which ΔH° has been estimated as 150 ± 20 cal mol^–1) and from rotation about the O–alkyl bond in isobutyl formate (for which ΔH° has been estimated as 745 ± 40 cal mol^–1).