Bonding in singlet and triplet butalene: insights from spin-coupled theory

J Phys Chem A. 2015 Mar 12;119(10):2169-75. doi: 10.1021/acs.jpca.5b00522. Epub 2015 Feb 25.

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.

MeSH terms

  • Models, Molecular
  • Molecular Conformation
  • Polycyclic Aromatic Hydrocarbons / chemistry*
  • Quantum Theory*
  • Thermodynamics

Substances

  • Polycyclic Aromatic Hydrocarbons