Dynamic NMR as a Nondestructive Method for the Determination of Rates of Dissociation. XIII. Sulfur Inversion in 9,9-Dialkyl-10-mesitylthioxanthenium Salts

Abstract

Abstract The sulfur-inversion in the title compound (alkyl=ethyl) was found to take place with the following activation parameters by dynamic NMR spectroscopy: ΔH\eweq=23.8±0.2 kcal mol−1, ΔS\eweq=2.6±0.4 cal mol−1 K−1. The significance of the near zero entropy of activation is discussed. The mesityl group in the title compounds also showed restricted rotation of which barrier to rotation was estimated to be 14 kcal mol−1 at 318 K for the compound where the alkyl is a methyl.