Spectral investigation of intramolecular interaction in sulfur-organic compounds

Earlier¹ it was reported that 4-aryl-4,5-dihydrothiophene-1,1-dioxides (I) are converted in aqueous and alcohol solution of bases to isomeric 3-aryl-2,5-dihydrothiophene dioxides (II) and 3-aryl-4,5-dihydrothiophene-1,1-dioxides (III) (Fig. 1).In the presence of electron-donor substituents in the p-position of the phenyl ring, IIb, c compounds are practically irreversibly isomerised to III b, c. For unsubstituted phenyldihydrothiophene-1,1-dioxides IIa and IIIa the reaction proceeds riversibly but equilibrium is shifted towards isomer IIIa indicating its high thermodynamic stability. It is known² that 2,5-dihydrothiophene-1,1 -dioxide is more stable than 4,5-dihydrothiophene-1,1-dioxide. Consequently, the observed stability increase of 3-aryl-4,5-dihydrothiophene-1,1-dioxides (IIIa–c) is due to interaction of the substituent C₆H₄X with the sulfonyl group. This paper investigates the nature of this interaction.