Conformations of some αβ-unsaturated carbonyl compounds. Part III. Infrared solution spectra of methyl, [2H3]methyl, ethyl, and [2H5]ethyl acrylates and trans-crotonates

Abstract

Infrared spectra of methyl, [²H₃]methyl, ethyl, and [²H₅]ethyl acrylates and trans-crotonates in solution in carbon disulphide are reported. Band intensity measurements at temperatures between –110 and 35 °C together with changes in the appearance of these bands on solidification of the solution are interpreted in terms of conformational equilibria between high- and low-energy forms. The additional enthalpies (ΔH°) of the high-energy forms are remeasured for methyl acrylate as 326 ± 18 cal mol^–1 and for methyl trans-crotonate as 306 ± 30 cal mol^–1. The additional entropy (ΔS°) of the high-energy form of methyl trans-crotonate is estimated as 1·5 ± 1·0 cal mol^–1 K^–1.