Kinetic and thermodynamic aspects of the retro cheletropic reaction of sulfur dioxide extrusion have been investigated. The interaction of the X-S bond (X=NH, S, O and CH2) and oxygen lone pairs of SO2 showed remarkable stereoelectronic effects and its correlation with the difference between computed and empirical bond length (Δl) have been analyzed. The facility of the reaction in the case of four derivatives(X=NH, S, O and CH2) has been investigated from the viewpoint of product delocalization energy. In addition, the substitution effects have been studied on the relative the Gibbs free energy of reaction for oxygen derivative (X=O). Moreover, a correlation between the Gibbs free energy of the reaction in the presence of the substituent and Δl as a criterion for the value of interaction between the X-S bond and oxygen lone pairs of SO2 group has investigated. Finally, a new different method base on electron density have been used for evaluation of the synchronicity values of the reaction. According to the corresponding diagrams, calculated synchronicity values of the Wiberg and electron density are in good agreement.

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