N-hydroxy-monomethoxy-4-aminoazobenzenes:: a computational study

Structures and electronic properties of the N-hydroxy metabolites (N-OH-OMe-AAB) of the monomethoxy-4-aminoazobenzene dyes (OMe-AAB) have been calculated using density functional theory with a basis set that includes polarization functions on all the atoms. Positional isomers with the methoxy group ortho to the hydroxyamino group (N-OH-3(5)-OMe-AAB) are found to be lower in energy than isomers with the methoxy group meta to the hydroxyamino group (N-OH-2(6)-OMe-AAB). The geometrical parameters of the phenyl rings for the corresponding isomers of OMe-AAB and N-OH-OMe-AAB are very similar. The length of the C-NHOH bond, however, is significantly longer than the length of the C-NH2 bond. The energies of the frontier orbitals are more negative for each of the positional isomers of N-OH-OMe-AAB than for the corresponding isomer of OMe-AAB. in particular, the energy of the lowest unoccupied molecular orbital decreases a few kcal/mol for each isomer, suggesting that these N-hydroxy metabolites are slightly more electrophilic. (C) 2001 Elsevier Science Ltd. All rights reserved.