A quantumchemical study of the C₆H⁺₅ potential energy surface. Evidence for a nonclassical pyramidal carbenic species

MINDO/3 and STO‐3G MO calculations including geometry optimization have been performed for nonlinear C 6 H + 5 structures. The phenyl cation 5 is the lowest energy compound on the surface, followed by the nonclassical pyramidal carbenic structure 4 . Other local minima include the bicyclic carbene 6 and the benzvalenyl cation 7 . Fairly good agreement between the results from both methods was obtained. The electronic structure of 4 is explained using orbital interaction diagrams which show the stabilization of the cyclopentadienyl cation by the apical carbon atom and the relation between 4 and pyramidal transition‐metal complexes. The electronic structure of 6 is related to that of the bicyclo[3.1.0]hexenyl cation 12 . Activation energies for rearrangement reactions on the energy surface show that 4 can probably be studied starting from benzvalene‐type precursors.