Energetics of hydrocarbon branching

The energetic stabilization of branched hydrocarbons relative to the corresponding normal isomers is investigated at both the molecular and atomic levels. n-Butane and isobutane and n-pentane and neopentane are studied as pairs that show preferential stabilization of the branched isomer. It is well shown that branching leads to an increased proximity of the atoms within the molecule, despite an increase in bond lengths. It is the greater proximity that causes a greater stabilization through an increase in the attractive energies of the molecule as well as the atoms. The overall stabilization is a result of the dominance of the gain in attractive energies over the increase in repulsion energies. This is demonstrated at both the atomic and molecular levels using the results of molecular and atomic quantum mechanical calculations.