Conformations of some αβ-unsaturated carbonyl compounds. Part IV. Infrared spectra of dimethyl, diethyl, and di-n-butyl fumarates and maleates

Abstract

I.r. spectra of dimethyl, diethyl, and di-n-butyl fumarates and maleates are reported. The effects on these spectra of cooling the liquids and their solutions in carbon disulphide to –100 °C and of solidification have been studied. For dimethyl fumarate the effects of heating the solid and its solution in carbon disulphide to +110 °C have also been studied. Evidence is presented for a conformational equilibrium in the fumarates involving probably trans–trans⇌trans–cis; ΔH°= 372 ± 20 cal mol^–1 was measured for di-n-butyl fumarate. The maleates probably exist in the cis–trans conformation.