An electronic properties investigation to interpret the substituent constants of monosubstituted benzene derivatives

In the present work, the pi and pi*-electronic nature of substitution constants (sigma) of the twenty-two monosubstituted benzene derivatives (MSBDs) are estimated in terms of the para-delocalization index (PDI) and total non-Lewis structure (TNLS), respectively. Since these compounds are aromatic, the other descriptors of aromaticity such as nuclear independent chemical shifts and aromatic stabilization energy have been examined. Because of no considerable variation for the pi and pi*-electron delocalization in the ring systems, a very weak correlation has been demonstrated between all aromaticity indices. Also, none of these descriptors has a linear correlation with the values of sigma for both electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) in a simultaneous relationship. We now propose the usage of the dipole moments values of molecules, considering their directions, by multiplying the PDI and TNLS values as probes to interpret sigma values for benzene and MSBDs since the dipole moment can affect the pi and pi*-electron delocalization. It is interesting to note that there is a remarkable linear correlation between our suggested probes, +/-mu PDI and +/-mu TNLS, and sigma(p), sigma(m), and sigma(+)/sigma(-) for EDGs and EWGs in simultaneous linear relationships. Also, these probes have a relative relationship with Kirkwood and Westheimer equation. Additionally, the regression coefficient between +/-mu PDI and +/-mu TNLS is 0.989. (C) 2019 Elsevier Inc. All rights reserved.