The C∼C bonds of the hydrocarbons provide the broadest range of bond orders and bond energies and thus provide the most rigorous test of the BEBOP concept. We supplemented the 41 hydrocarbons and radicals of the G2/97 test set with 15 additional species such as the C -H 4 Σ excited state (to test the BEBOP treatment of hybridization), calicene (to test the ability of the BEBOP model to handle charges), and tetrahedrane (to push the limits of ring strain).