Ground states of conjugated molecules XVI. Treatment of hydrocarbons by l.c.a.o. s.c.f. m.o

Abstract
Previous work in these laboratories has led to the development of a semi-empirical s.c.f. m.o. treatment of conjugated hydrocarbons which enables their heats of formation and geometries to be predicted with surprising accuracy. Problem s have arisen, however, in attempts to extend this treatment to compounds containing heteroatom s, mainly because of the thermo ¬ cycle method used to estimate the one-electron resonance integrals (ß). H ere we report a simpler version of the treatment, based on the Mulliken approximation (ß = KS), which gives equally good results and should be more easily applied to heteroconjugated molecules. A procedure for including non-bonded interactions in the treatment is described and illustrated by a study of the rotation al barriers in biphenyl and 1,3-butadiene.