A Differential Molecular Connectivity Index

A differential molecular connectivity index, ΔmX, has been defined which is the difference between the simple and the valence connectivity indexes of the same order, m, is ΔmX = mX — mXv. The information contained in this index is largely electronic with contributions from adjacent alkyl fragments amounting to the size of m. The electronic information is a quantitation of the pi and lone pair electrons on that part of the fragment defined by m. The index is capable of modeling selected physical properties which are regiospecific within a molecule. Examples include NMR chemical shifts, gas phase basicities, ionization potentials and chromatographic retention indexes.