Physicochemical Properties of 1, 3-Dithiol-2-ylidene and 1, 3-Oxathiol-2-ylidene Derivatives

The influence of the contribution of the dipolar form to the resonance hybrid structure on the chemical stability of 1, 3-dithiol- and oxathiol-2-ylidene derivatives was investigated by means of infrared, ultraviolet, nuclear magnetic resonance, and dipole moment measurement. It is concluded that though the contribution of the polar form to the resonance hybrid is small, it is nevertheless important for double bond isomerization through nonbenzenoid aromatic stabilization of its positive charge. Protonation of the double bond in acid medium does not necessarily occur, since some of the title compounds are not Hammett bases.