Electronic properties of N-heteroaromatics. XLI. Charge-transfer interactions of the carcinogen 4-nitroquinoline 1-oxide with methylsubstituted benzenes and methylsubstituted aniline derivatives

Abstract

With the object of examining the π-acceptor property of carcinogenic 4-nitroquinoline 1-oxide, spectrophotometric examination was made on the interaction of the N-oxide compound with a variety of methyl substituted benzenes and anline derivatives. The following results were obtained through analysis of the new absorption bands which appeared in the visible difference spectra of mixed systems of the above derivatives and the N-oxide compound : (1) Absorption maxima of the difference bands shifted toward a longer wavelength region with increasing polarity of the solvents. (2) There was a linear relationship between IP values of the methyl substituted benzenes and aniline derivatives and hv values of the absorption maxima. (3) It was confirmed that complexes of 1 : 1 molar ratio were formed by the interaction. (4) A corresponding relationship was found to exist between K values of the methyl substituted benzene-N-oxide compound complexes and IP values of the substituted benzenes. (5) The K values of the aniline derivative-N-oxide compound complexes were affected markedly by the steric effect of substitutent methyl groups. (6) Analysis of the pH effect indicated that the uonionized species of aniline derivatives were more favorable for the interaction. Based upon these results (1-6), it was presumed that π-π type and n-π type charge transfers were involved in the interaction of 4 -nitroquinoline 1-oxide with methyl substituted benzenes and aniline derivatives. The magnitude of ΔH values was consistent with this presumption. It was also found that the carcinogenic quinoline compound is a stronger π-acceptor than non-carcinogenic 4-nitropyridine 1-oxide.