Theoretical energies of representative carbon-carbon bonds

A bond-energy formula deduced by means of the Hellmann-Feynman theorem is applied to selected simple hydrocarbons. The required potentials at the nuclei are calculated with the help of large basis-set expansions including polarization functions. The carbon-carbon bond energy of ethane is evaluated at ∼ 70 kcal mol-1. The cc bond energies of ethane, ethylene, acetylene, benzene, and cyclopropane are approximately in a ratio of 1:2.0:3.0:1.65:1.0. Limitations and possible improvements in future applications of this energy formula are discussed. 33 refs., 3 tabs