Quantum chemical study of the structure of bicyclo[2.2.0]hex-1(4)-ene and its dimers

The RHF, B3LYP, and PBE0/6-311G** quantum chemical methods are used to determine the point symmetry group and the equilibrium structure of bicyclo[2.2.0]hex-1(4)-ene (I, D 2 h ), its two stable dimers (tricyclo[4.2.2.2 2,5 ]dodeca-1.5-diene (II, D 2 h ) and 2,5-dimethylenetricyclo[4.2.2.0 1,6 ]decane (III, C 2 )), and pentacyclo [4.2.2.2 2,5 ]dodecane (IV, D 2 ) that is a hypothetical intermediate in the dimerization reaction of the molecules of I. The relation of total energies is obtained with regard to zero-point vibrations: E (III) < E (II) ≪ E (IV) ≪ 2 E (I).