An atom-bond connectivity index: Modelling the enthalpy of formation of alkanes

The atom-bond connectivity index (ABC), a novel graph theoretical invariant , based on the connectivity between atoms and bonds in a molecule, is propo sed. This structure-descriptor is computed from the vertex and edge degrees , but in contrast to the original connectivity index of Randic - ABC does n ot reflect the extent of branching of the molecule. ABC is used to describe the heats of formation of alkanes, resulting in a good quantitative struct ure-property relationship (QSPR) model ( r = 0.9970). The model is interpre ted in such a manner that the intercept and slope of the regression equatio n have a physical meaning.