General definition of valence delta-values for molecular connectivity.

The molecular connectivity valence delta-values have been defined in terms of the count of nonhydrogen valence electrons on a valence-state atom as screened from the nucleus by the core electrons. The core is defined as the nonvalence electrons minus 1. This general definition expresses the valence delta-values for second and third quantum level atoms and halogens. Valence delta-values have been derived for higher oxidation states of sulfur and phosphorus. The internal consistency of these delta-values is tested by their ability to closely correlate molar refraction values with 1 chi v. It is found that a second variable, the count of the number of alpha hydrogen atoms, greatly increases the quality of the correlation. Some biological SAR applications reveal the general utility of these findings.