Knowledge Bank

Previous work has supported the thesis that the bands of benzene are displaced and occur in the spectra of its simple monosubstituted and disubstituted derivatives. The wavelength position of the bands of these derivatives is roughly predictable. The concepts evolved have now been applied to certain types of trisubstituted benzene compounds containing one electron attracting and two electron releasing substituents. The spectra of these trisubstituted derivatives have been compared with the spectrum of each of the possible disubstituted compounds containing the same substituent groups in the same relative positions in the benzene ring. It has been found that a striking similarity frequently exists between the spectrum of a trisubstituted derivative and that of the most displaced of the corresponding disubstituted compounds. This applies both to the general appearance of the spectrum and to the wavelength position of the bands. The correspondence in position is particularly good with the first primary band (the ca. $200-\mu$ band in benzene itself). Certain limitations and consequences of this generalization will be discussed.