CONFORMATIONAL STUDY AND GROUND-STATE DIPOLE-MOMENTS OF 2 KETENE DITHIOACETAL COMPOUNDS

Dipole moments (mu) of methyl-2-(1,3-dithietan-2-yliden)-3-oxobutanoat e (1) and methyl-2-(1,3-dithiolan-2-yliden)-3-oxobutanoate (2) were me asured in benzene solutions. Calculations of mu were performed using b oth the quantum chemical semiempirical PM3 method and the bond moments additivity model with additional electrostatic interaction calculatio ns in the case of zwitterionic forms. A comparison of calculated value s with the experimental ones shows that the electronic delocalization is larger for 2 than for 1 and more pronounced in the solid state than in solution for both molecules, in qualitative agreement with their f irst nonlinear polarizabilities beta(2 omega). (C) 1997 Elsevier Scien ce B.V.