BOND POLARITY INDEX - APPLICATION TO GROUP ELECTRONEGATIVITY

In spite of its potential usefulness to synthetic and structural chemists, there has been no consensus on a quantitative group electronegativity scale nor a manifestation of confidence in existing definitions. The present effort seeks to resolve this problem by (1) employing the bond polarity index, BPI(AB), a simple, well-defined quantum mechanical measure of the one-electron energy difference between adjacent atoms A and B in a molecule and (2) demonstrating an excellent correlation between BPI(AB) and experimental results from electron spectroscopy for chemical analysis (ESCA) core-electron binding energies, the most readily interpretable measurements of substituent electron withdrawal. Correlation with substituent constants (F and sigma(F)), two other relevant experimental measures, is also good. Correlations with C-13 NMR chemical shifts and 1J(cc) coupling constants, previously proposed as measures of group electronegativity, have been investigated and comparisons with other definitions of group electronegativity are included.