Conformations of some αβ-unsaturated carbonyl compounds. Part VII. Assignments of Raman and infrared spectra of dimethyl, diethyl, and di-n-butyl fumarates and maleates

Abstract

Raman and i.r. spectra of dimethyl, diethyl, and di-n-butyl fumarates and maleates in the liquid (or solid) state at room temperature (or above) and as frozen solids are reported together with vibrational assignments for conformers (trans,trans⇄trans,cis for the fumarates, cis,trans only for the maleates). Measurement of intensities of selected Raman bands at various low temperatures leads to calculation of enthalpy differences (ΔH⁰± standard deviation) of 396 ± 42 and 219 ± 28 cal mol^–1 between the high and low energy forms of the di-n-butyl and diethyl fumarates, respectively. Dimethyl fumarate is a solid at room temperature; measurement of Raman band intensities at higher temperatures leads to a corresponding value of 774 ± 184 cal mol^–1. These results provide general support for a previous result based on i.r. measurements.