The vibrational spectra, conformational and thermodynamic properties of 2-chlorobuta-1,3-diene (chloroprene) and propenoyl chloride

Abstract

The vibrational spectrum of 2-chlorobuta-1,3-diene has been recorded in the gaseous, liquid, solid and solution phases, and also in an argon matrix. Several weak bands present in the i.r. spectrum of the fluid phases and unannealed matrix were observed to be absent after careful annealing. Thermodynamic functions for the ideal gas have been estimated from those of other compounds, and their values, taken together with the spectral changes on annealing, are concluded to be evidence of a conformational equilibrium. The most probable molecular structure has been calculated using previous microwave data, and the asymmetric potential function to internal rotation has also been calculated using a value of Δ H θ of 8.2 kJ mol −1, as derived by statistical methods. The i.r. spectrum of gaseous propenoyl chloride has been recorded to aid in assignment of the spectral features of the isoelectronic compound 2-chlorobuta-1,3-diene, and improved vibrational assignments of both compounds are presented. New values for the thermodynamic functions of propenoyl chloride are presented to take into account the significant changes made to the vibrational assigmnent.