Orientation effects in the benzene chromophore bearing one donor and two acceptor groups. Electronic absorption spectra of the dicyanoanilines

Abstract

The light absorption properties of the benzene chromophore substituted with one donor (+M) and two acceptor (–M) groups have been investigated using the dicyanoanilines as model compounds. The absence of strong steric ortho-interactions and intramolecular hydrogen bonding enables the dependence of the wavelength of the first absorption band on substitution pattern to be determined. The syntheses of the two remaining members of this series, 2,4- and 2,6-dicyanoaniline, are described. The observed influence of the position of the cyano-groups on λ_max. order was : 2,5 > 2.3 > 2,6 > 3,5 > 3.4 > 2,4, and cannot be explained in terms of resonance theory. However, the PPP SCF-Cl molecular orbital method predicted this wavelength dependence accurately.