Graph Theory and Structure-Aromaticity Relationships

摘要

Three-dimensional aromaticity is now well-established in the deltahedral boranes as an extension of the familiar two-dimensional aromaticity in benzene and related aromatic hydrocarbons. Moebius aromaticity, in which the π-electron network is twisted as in a Moebius strip, can be postulated to occur in the five-center four-electron bond in the equatorial pentagon of pentagonal bipyramidal RhBi_7(μ-Br)_8. This delocalized bonding in RhBi_7(μ-Br)_8 can be contrasted with the localized bonding in the ions [RhBi_6(μ-X)_(12)]~(3-) (X = Br, I). Another type of aromaticity is the σ-aromaticity found in cyclopropanes. σ-Aromaticity can also account for the stability of triangular metal carbonyls such as M_3(CO)_(12) (M = Fe, Ru, Os) relative to square metal carbonyls such as Os_4(CO)_(16).