Matrix effects in the infrared spectra of cyanoethene (acrylonitrile) and 2-chlorobuta-1,3-diene (chloroprene)

Abstract

I.r. spectra of matrix-isolated forms of acrylonitrile and chloroprene are reported. The twisting mode of the vinyl group in the 970–990 cm^–1 region reveals considerable splitting in each compound which is attributable to high and low energy forms. Measurements are reported on rate of change from high to low energy forms compared between 1 : 500 and 1 : 5 000 dilutions in argon in both compounds at 35 K. The results confirm the low energy form is a polymeric aggregate in the case of acrylonitrile but arises from an intramolecular effect in chloroprene. First-order rate constants were estimated for acrylonitrile and chloroprene at low and high dilutions. Assignments to high and low energy forms are presented between 400 and 3 500 cm^– in each case and the structures of these forms are discussed.