Ab initio study of the conformations of chloromethyl formate and fluoromethyl formate

Ab initio calculations are reported for the conformational potential energy surfaces of chloromethyl formate and fluoromethyl formate at minimal basis set level. The halomethyl group is shown to lie Z to the carbonyl group. A plateau on the potential energy surface demonstrates that the halomethyl group can rotate freely. The halogen atom therefore moves from an antiperiplanar (ap) to a synclinal (sp) position with respect to the carbonyl group. The effects on IR spectra and dipole moments are discussed.