Aspects of acyclic azine chemistry -- I. The effect of structure and solvents on the electronic absorption spectra of benzaldazine, o-, m- and p-hydroxybenzaldazines

Article abstract of DOI:10.1016/0584-8539(80)80117-6

The electronic absorption spectra of benzaldazine, o-, m-, and p-hydroxybenzaldazines have been separately examined in various solvents (20 solvents and solvent mixtures).The observed three groups of bands designated as α (200-225 nm), β (289-307 nm) and γ (352-375 nm) are attributed to ?* <-- ? transitions although experimental evidence based on spectra obtained in concentrated sulphuric acid reveals that ?* <-- ?(n) transitions constitute part of the γ-band.On the basis of group theoretic analysis, in the singlet manifold, all ?* <-- ?(n) transitions (i.e. ^IA_u <-- 1^IA_g) are out-of-plane (Ξ) polarized while all ?* <-- ? transitions (i.e. ^IB_u <-- 1^IA_g) are in plane (x,y) polarized.In the rationalization of data, the theory of resonance has been employed where deemed useful.The shifts of bands with solvents have been traced.