Abstract Dipole moments of fifteen 2, 4-substituted4-N, N-dimethylamino-3-aza-1-thia (oxa) butadienes were measured in carbon tetrachloride solution. Calculations of molecular moments for five compounds in the sp (C S and N C on the same side) and ap conformations were performed according to the bond moment model. A comparison of calculated values with the experimental ones shows that the sp conformation is favoured ...