SUBSTITUTED 1-HETERO-3-AZA-1,3-BUTADIENES - DIPOLE-MOMENTS AND RELATED STRUCTURAL-ANALYSIS

Dipole moments of selenobenzamide, of eight N'-thio toro or seleno) ac ylamidines and of two N'-thioacyliminoethylidenetriphenylphosphoranes in carbon tetrachloride, benzene or dioxane solutions were measured or examined. Calculations of molecular moments for the sp (C=S and N=C o n the same side) and ap conformations and for the canonical structures implied by conjugation were performed according to a recently propose d method. A comparison between the calculated and the experimental val ues shows that only strong conjugations with significant statistical p ercentages p(s)(+/-) of the 1,5 (or 1,6) zwitterionic forms (X(-)-C=N- C=N+ or X(-)-C=N-C=C-P+ with X = 0, S or Se) can explain observed mome nts. The mu differences between compounds are related to p(s)(+/-) var iations which can give information about the molecular structures and their relationship with reactivities.