Molecular optical rotation: an evaluation of semiempirical models

Ab initio optical rotations have been obtained for allene, 1,3-dichloroalle ne, H2O2, and H2S2 as a function of dihedral angles, both at SCF and post-S CF levels. The results have been used to test (a) the concept that the mole cular optical rotation can be written as a Sigma(i) M-i sin theta(i), where theta(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 strong ly on the level of ab initio theory used, so highest levels of theory are r equired for accurate predictions. The optical rotation patterns obtained us ing high-level ab initio theory for H2O2, H2S2 and allene, as a function of dihedral angles, are found to be in line with Kirkwood's polarizability mo del predictions but not with the Sigma(i) M-i sin theta(i) predictions. (C) 2000 Elsevier Science B.V. All rights reserved.