Vibrational Spectra and Rotational Isomerism in Acrylyl (Propenoyl) Chloride and Related α,β-Unsaturated Acyl Halides

The complete vibrational spectra of acrylyl (propenoyl) chloride have been recorded and analyzed. This compound exists as a mixture of two discrete rotational isomers in the vapor and liquid states, their energy differing by about 0.6 kcal/mole in the vapor state. The spectra of the two isomers have been tentatively assigned and it has been found that all of the skeletal stretching modes are conformation dependent. Three other α,β-unsaturated acyl chlorides have been studied and the results are compared with those of acrylyl chloride.