Conformational stability, barriers to internal rotation, ab initio calculations and vibrational assignment of dichloroacetyl chloride

Abstract

The Raman (3100−10 cm−1) and infrared (3100−30 cm−1) spectra of dichloroacetyl chloride, CHCl2CClO, in the gas and solid phases have been recorded. Additionally, the Raman spectrum of the liquid and the qualitative depolarization ratios have been obtained. From these data a gauche/trans equilibrium is proposed in the gas and liquid phases, with the gauche conformer being the more stable form in both physical states and the only form present in the annealed solid. From the study of the Raman spectra at different temperatures, values of 56±5 cm−1 (160±14 cal mol−1) and 131±32 cm−1 (376±90 cal mol−1) were determined in ΔH of the liquid and gas, respectively. A potential function for the conformational interchange is suggested.A complete vibrational assignment is proposed for both conformers based on infrared band contours, Raman depolarization data, group frequencies and normal coordinate calculations. The experimental structural parameters, conformational stabilities, barriers to internal rotation, and fundamental vibrational frequencies are compared with those obtained from ab initio Hartree—Fock gradient calculations employing both the RHF/3-21G* and RHF/6-31G* basis sets, and to the corresponding quantities obtained for some similar molecules.