Isomers of Benzene on Its Global Network of Reaction Pathways

Isomers of benzene (C6H6) have been searched by quantum chemical calculations using the GRRM/SCC-DFTB program. Further optimization at the level of B3LYP/6-311G(d,p) gave 2004 equilibrium structures (EQ). Obtained EQs were assigned as 212 valence isomers, 928 nonvalence isomers, 798 two-component clusters, and 66 three-component clusters. Energies of EQs range from the most stable isomer of benzene to the highest EQ at 1237 kJ mol−1. The low energy region below 380 kJ mol−1 only includes valence isomers. Valence isomers are distributed between 0 and 807 kJ mol−1, while nonvalence isomers are located in the range of 380–1180 kJ mol−1. All of the experimentally known 30 isomers of benzene were searched as valence isomers by the ADDF/SCC-DFTB method. Formally hypervalent molecules including pentacoordinated carbon atoms were discovered among nonvalence isomers.