The E-State as an Extended Free Valence

The relationship between the electrotopological state index (E-state) and the molecular orbital based index of free valence is examined. The dependence of both on electronegativity and topology are developed from comparative values. Calculations of both indices for a diverse set of conjugated carbons reveal a significant correlation. Since the E-state index is calculated for heteroatoms and all σ bonded atoms, it represents an extention of the concept of free valence applied to all atoms in a molecule.