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.