Rotational isomerism. Part VIII. A calculation of the rotational barriers and rotamer energies of some halogenated compounds

Abstract

A method is suggested for calculating internal rotation barriers and rotamer energy differences in halogenated ethane-like molecules. The total interaction energy in a Particular orientation is given by the summation of all steric and electrostatic interactions between non-bonded atoms plus a torsional term which is directly related to the intrinsic barrier to rotation in ethane. The electrostatic term includes all hydrogen–halogen attractive interactions besides the halogen–halogen repulsions. The derivation of parameters to describe the various interactions together with the selection of a consistent set of molecular geometries is discussed. The model reproduces barrier heights and rotamer energy differences of a large number of molecules satisfactorily. The consequences and limitations of the model are critically assessed.