APPROXIMATIONS IN ONE-ELECTRON THEORY OF OPTICAL ROTATION

The one-electron theory is applied to L-3-aminopyrrolid-2-one. The rotatory strength of the nπ* transition Rao is evaluated with various models of the amide chromophore and of the perturbing amino group. It is found that: (1) Ra0 is very sensitive to the degree of delocalization of the nonbonding orbital of the amide oxygen; (2) in the perturbation treatment the transition charge distribution in the amide group is well represented by point quadrupoles on oxygen and carbon, the next higher, 26-pole, terms making only a small contribution to Ra0 (3) the perturbing electrostatic field, as derived from the ground-state electron density of the amino group, is fairly well represented by partial charges on the nuclei, except at very short distance; (4) the representation of all overlap charges in the amino group by point monopoles, an elaboration of a method introduced by London, gives a perturbing field that is about five times too high.