Conformational analysis of dichloromethyl formate by the combined use of infrared and matrix-infrared spectroscopy and ab initio calculations

Abstract

The conformations of dichloromethyl formate (HCOOCHCl₂) was studied in the gas, liquid, and crystalline phases and in a low-temperature argon matrix by infrared spectroscopy. The experimental results, supported by RHF/and MP2/6-311++G** ab initio calculations, show that the same single conformer, Z,quasi-sp, is present in each of these states. The Z,quasi-sp conformer belongs to the C₁ point group and the two dihedral angles, OC–O–C and C–O–C–H_alkyl, are locked in planar Z and near-planar orientations, respectively, calculations providing a value of 23° for the latter angle. Altogether, a total of four conformers, Z,quasi-sp; Z,ap; E,sc; and E,ap, were calculated to represent local minima on the potential energy surface, but consideration of their relative energies implies that it is only the Z,quasi-sp conformer which would give rise to observable spectral lines. The complete assignment of the fundamental infrared bands of this conformer has been made based on the potential energy distributions obtained from normal coordinate calculations performed on both dichloromethyl formate and its dideuterated derivative.