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.