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 .