The molecular orbital theory of chemical valency. XI. Bond energies, resonance energies and triplet state energies

Abstract The expression for the total energy of a saturated molecule is discussed. It is shown that it can be written as the sum of suitably defined bond energies. The total energy of a con­jugated molecule is not additive but can be expressed as a sum of bond energies together with a resonance energy which can be calculated by means of the standard excited state approximation. For hydrocarbon molecules, by a series of coincidences, this method leads to the same expression for the resonance energy as the Hückel method. A method of cal­culating the energies of some of the ground state-triplet transitions of conjugated molecules is also described. The energy of the phosphorescence transition is calculated for some hydrocarbon molecules and is in good agreement with experiment.