title: Bonding in singlet and triplet butalene: insights from spin-coupled theory.
abstract: Spin-coupled (SC, equivalent to full generalized valence bond) calculations for the (1)A(g) ground state of butalene at its optimal D(2h) planar geometry show that cross-ring Dewar-like modes of spin coupling are of comparable importance to the more usually considered Kekulé-like modes. There are marked similarities to the SC description of one of the isomers of benzo[1,2:4,5]dicyclobutadiene. A complication for both of these systems is the existence of SC solutions in which some of the orbitals resemble in- and out-of-phase combinations of semilocalized atom-centered orbitals. The lowest triplet state, for which a nonplanar C(2v) geometry is preferred, is somewhat more straightforward to analyze: the SC description of the (3)B2 state is dominated by a very simple pattern of two π bonds and two well-localized triplet-coupled orbitals.
authors: Department of Chemistry, University of Liverpool , Liverpool, L69 7ZD, U.K.
authors: David L
authors: DL
authors: Cooper
authors: Peter B
authors: PB
authors: Karadakov
authors: Brian J
authors: BJ
authors: Duke
mesh_terms: D008958:Models, Molecular; D008968:Molecular Conformation; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D011084:Polycyclic Aromatic Hydrocarbons