Valence isomers of benzene and their relationship to isomers of isoelectronic P6

Abstract

We report the results of geometry optimized ab initio SCF MO calculations with 3-12G, 4-31G*, and 6-31G* basis sets for neutral P 6 in forms corresponding to the five valence isomers of benzene, (CH 6 ), with which P 6 is valence isoelectronic. At the 6-31G* level benzene, Dewar benzene, benzyvalene, prismane, and bicyclopropenyl structures all correspond to real minima on the P 6 energy surface. The order of energies of P 6 structures is quite different from that for the (CH 6 ) isomers. For P 6 , benvalence and prismane have low energies and the planar hexagon has the highest. Bond distances are easily classified as single, double, or aromatic. The energy of 2P 6 lies only 30-35 kcal/mol above that of 3P 4 and 60-100 kcal/mol below 6P 2