m-Benzyne and bicyclo[3.1.0]hexatriene – which isomer is more stable? – a quantum chemical investigation

Density functional theory (DFT) predicts that bicyclo[3.1.0]hexatriene (2) is more stable than its isomer m-benzyne (1). Hess [Eur. J. Org. Chem. (2001) 2185] has argued that experimental findings suggesting 1 can equally or even better be associated with 2. However, high level ab initio calculations (CCSD(T), CASPT2) show that 2 does not exist and that the previously measured infrared spectrum is correctly assigned to 1. Bond stretch isomers are possible for p-benzynes but not for m-benzynes. The electrophilic character of m-benzynes is in line with 1 but not with 2.