Conformational study and ground state dipole moments of two ketene dithioacetal compounds

Abstract Dipole moments (μ) of methyl-2-(1,3-dithietan-2-yliden)-3-oxobutanoate ( 1 ) and methyl-2-(1,3-dithiolan-2-yliden)-3-oxobutanoate ( 2 ) were measured in benzene solutions. Calculations of μ were performed using both the quantum chemical semiempirical PM3 method and the bond moments additivity model with additional electrostatic interaction calculations in the case of zwitterionic forms. A comparison of calculated values 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 first nonlinear polarizabilities β(2ω).