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The MINDO/3 semiempirical SCF-MO method has been tested by calculations for a wide variety of hydrocarbons, for radicals and ions derived from them, and for several simple hydrocarbon reactions.The preceding paper1 described the development of an improved version (MINDO/3) of the MINDO3"5 semiempirical SCF-MO method. Here we report the results of calculations for a wide variety of hydrocarbons, for ions and radicals derived from them, and for several simple reactions of hydrocarbons.

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The stereochemical consequences of electron delocalization in substituted ethylenes (e.g., 1,2-difluoroethylene), propenes, butadienes and allyl and pentadienyl anions, as well as 1,2-disubstituted ethanes, are discussed. It is shown, on the basis of simple perturbation theory, that the generally greater stability of the bent (cis or gauche) conformations of these molecules may be attributed to a previously unrecognized conjugative destabilization which is transmitted through bonds and is greater for elongated, trans conformations than for bent, cis structures. This destabilization is due to the exchange (exclusion) repulsion associated with overlap between filled orbitals. The effect is conformation dependent in extended systems as a result of the fact that electrons delocalize preferentially in straight lines.