Pure Appl. Chem., 1993, Vol. 65, No. 1, pp. 35-45
doi:10.1351/pac199365010035
The delocalization of π electronic systems as a destabilizing constraint imposed by the σ frame. Allyl, benzene, cyclobutadiene and related heteroannulenes
P. C. Hiberty, G. Ohanessian, S. S. Shaik and J. P. Flament