Molecular optical rotation: an evaluation of semiempirical models

Abstract

Ab initio optical rotations have been obtained for allene, 1,3-dichloroallene, H 2O 2, and H 2S 2 as a function of dihedral angles, both at SCF and post-SCF levels. The results have been used to test (a) the concept that the molecular optical rotation can be written as a ∑ i M i sin θ i , where θ i is the dihedral angle of the ith X–A–A–X type segment and M i is a parameter associated with that segment; and (b) Kirkwood's polarizability model. The predicted ab initio optical rotation was found to depend strongly on the level of ab initio theory used, so highest levels of theory are required for accurate predictions. The optical rotation patterns obtained using high-level ab initio theory for H 2O 2, H 2S 2 and allene, as a function of dihedral angles, are found to be in line with Kirkwood's polarizability model predictions but not with the ∑ i M i sin θ i predictions.