The electronic and molecular structure of cyclopropane, isocyanomethane and isocyanocyclopropane

Ab initio SCF MO calculations have been carried out on cyclopropane, isocyanomethane and isocyanocyclopropane in order to elucidate the relative importance of σ-and π-electronic interactions between the substituent and the cyclopropane ring. Complete geometry optimizations have been carried out. The computed structures are in excellent agreement with experimental structure determinations. Bond lengths, gross charges and a detailed analysis of bond path gradients yield evidence of a conjugative interaction between the isocyano and the cyclopropyl group and a small hyperconjugative interaction in isocyanomethane. In addition, there is a considerable inductive electron flow from the hydrocarbon moiety to the nitrogen atoms as expected from electronegativity.