The conformational analysis of saturated heterocycles—XL

The rates of hydrogen-deuterium exchange of protons alpha to the sulphonyl group in a conformationally rigid sulphone have been measured in aqueous-DMSO. The exchange rate ratio k eq: k ax is 1·6. The greater kinetic acidity of the equatorial proton is in accord with recent MO calculations on sulphonyl carbanion stability, but does not preclude the intermediary of planar species.