Localized Bonds in SCF Wavefunctions for Polyatomic Molecules. III C–H and C–C Bonds

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Abstract
Localized molecular orbitals which minimize the exchange energy have been obtained for CH4, C2H6, C2H4, C2H2, CH3CCH, C3H6, HCN, and H2CO. These objectively determined orbitals correspond to the inner shells, lone pairs, and two‐center bonds of classical bonding theory. In each case where double or triple bonds occur, the local orbitals correspond to equivalent bent bonds. The hybrids in the C–C bonds of cyclopropane form angles of 28° with the internuclear direction. The local orbitals are analyzed in terms of hybridization, polarity, bond moments, bond directions, and delocalization. Calculation of the curvature of the self‐repulsion energy surface provides an indication of the uniqueness of the results. Sigma–pi separability and the sensitivity of the local orbitals to changes in basis set are also discussed.