Calculation of Hammett Equation parameters for some N,N′-bis (substituted-phenyl)-1,4-quinonediimines by density functional theory

Hammett parameters σ′ were determined from vertical ionization potentials, vertical electron affinities, adiabatic ionization potentials, adiabatic electron affinities, HOMO, and LUMO energies of a series of N,N′-bis (3′,4′-substituted-phenyl)-1,4-quinonediimines computed at the B3LYP/6-311+G(2d,p) level on B3LYP/6-31G∗ molecular geometries. These parameters were then least squares fit as a function of literature Hammett parameters. For N,N′-bis (4′-substituted-phenyl)-1,4-quinonediimines, the least squares fits demonstrated excellent linearity, with the square of Pearson’s correlation coefficient (r2) greater than 0.98 for all isomers. For N,N′-bis (3′-substituted-3′-aminophenyl)-1,4-quinonediimines, the least squares fits were less nearly linear, with r2 approximately 0.70 for all isomers when derived from calculated vertical ionization potentials, but those from calculated vertical electron affinities usually greater than 0.90.

► Hammett parameters were calculated for a series of quinonediimines.
► Parameters were then least squares fit to literature Hammett parameters.
► Substituent effects were more regular on the LUMO than on the HOMO.
► The greater regularity for the LUMO is consequence of the Hammond principle.