Naphthoquinone colouring matters. Part 3. Synthesis and electronic absorption spectra of 1,4-naphthoquinones containing electron donor groups in both rings

Abstract

The syntheses of several 1,4-naphthoquinones containing mesomeric electron donor groups (NH₂, NHR, or OMe) in both rings are described. The most convenient routes involve nucleophilic replacement of labile 2- or 3-substituents (Cl, Me, CN) in appropriately substituted 5-donor- or 5,8-bis(donor)-1,4-naphthoquinones. The directing effects of 5-amino- and 5-nitro-groups in these reactions have been examined. The electronic absorption spectra of the derivatives show a broad, complex band system in the 350–600 nm region, and PPP–MO catculations indicate that this results from two overlapping π-π* transitions, one involving electron density migration from the benzenoid donor-group(s) into the quinonoid system, and the other involving a similar transfer of negative charge from the quinonoid donor group(s).