Electrostatic potential minimum of the aromatic ring as a measure of substituent constant

The molecular electrostatic potential minimum (V-min) observed for the arene pi system of a substituted benzene derivatives is found to correlate linearly with the substituent constant sigma(p)degrees. The use of V-min as a measure of substituent effect is further confirmed by obtaining a linear correlation between V-min and a thermodynamic measure of the substituent effect obtained from an isodesmic reaction scheme involving benzene derivatives. V-min and the recently proposed electrostatic potential value at the nucleus of the para carbon atom (V-c) show a nearly identical trend toward quantification of substituent effects. Both quantities have been compared at three different density functional theory methods, viz. B3LYP/6-311+G(2d,2p), BPW91/6-311G(d,p), and B3LYP/aug-cc-pvtz, as well as the at the MP2/6-31+G(d,p) level of theory, showing remarkable consistency among them.