BORON PHOTOCHEMISTRY. XV. DETERMINATION OF THE HAMMETT SUBSTITUENT CONSTANT FOR THE p-DIMESITYLBORYL GROUP

Article abstract of DOI:10.1016/S0022-328X(00)86094-5

Hammett signal values reflect relative strengths of the combined inductive and resonance effects of substituents.Using the ionization technique, as well as an independent neutralization method, we found the ?_H value for the p-dimesitylboryl group to be 0.42 as compared to 0.78 for the p-nitro group.The value of ?_uv,H=0.65 +/- 0.03 determined from pi-electron interaction processes, such as absorption spectra and pi complex formation, is felt to relate better to the p-dimesitylboryl-substituted dyes.A similar function reflecting the pi resonance interaction of substituent groups is the Tomasik-Krygowski ?_uv,K value, for which 0.58 was found for the p-dimesitylboryl group compared to 0.66 for the p-nitro group.