Theoretical study of prototropic tautomerism and acidity of tris(fluorosulfonyl)methane

Abstract The prototropic tautomerism and acidity of (FSO 2 ) 3 CH was studied at both the semiempirical (PM3) and ab initio (HF/STO-3G∗ and 3–21G∗) level. It was shown that PM3 fails to describe the energetics of prototropic tautomerism, while giving the geometry of the sulfo form in good agreement with the experimental data. The ab initio calculations predict, in accordance with the experiment, that the sulfone form is more stable than the enol form. The conformity between calculated and experimental geometry was also satisfactory. The gas phase acidity of (FSO 2 ) 3 CH was calculated and the factors which contribute to the extremely high gas phase acidity of the title compound were discussed.