Vibrational spectra and rotational isomerism of methyl and ethyl cyanoacetate

Abstract

The infra-red absorption spectra of liquid and solid methyl cyanoacetate and ethyl cyanoacetate have been examined. For the methyl ester, evidence is found of rotational isomerism arising from internal rotation about the NCH₂C—C bond. The enthalpy difference between the two stable rotameric forms (with the CN group cis and gauche to the CO bond) was found to be 4060 ± 300 J mol^–1.

For ethyl cyanoacetate, the infra-red spectrum suggests the presence of several rotamers brought about by rotation about both the NCH₂C—C and the O—C₂H₅ bonds.