Rotational Spectra of Cis and Trans Crotononitriles

Abstract

The rotational spectra of the ground vibrational state of the cis and trans isomers of crotononitrile have been measured in the frequency region of 6-420 GHz. Accurate rotational and centrifugal distorsion constants, and nuclear quadrupole coupling constants have been determined for both isomers. A barrier height of 1387.2(8) cal/mol for the internal rotation of the methyl group of cis-crotononitrile was obtained from the analysis of the splittings. An ab initio structure has been calculated for both forms (as well as for isomers) and a near-equilibrium structure has been estimated using offsets derived empirically.