Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. IV. The Temperature Dependence of the Deuterium Effect for the Reaction of <i>N,N</i>-Dimethyl-<i>d</i>₆-aniline and Methyl <i>p</i>-toluenesulfonate. Correlation of Isotope Effects on Activation Parameters

Abstract

The temperature dependence of the isotope effect for the reaction of dimethylaniline and dimethyl-d 6 -aniline with methyl p-toluenesulfonate in nitrobenzene solvent has been measured, yielding the result, (ΔH D * − ΔH H *) = −134 ± 30 cal mole −1 , (ΔS D * − ΔS H *) = −0.15 ± 0.09 cal mol –1 degree −1 .This result has been compared with 15 other temperature dependence studies by plotting ΔΔH* per D atom vs. TΔΔS* per D atom. The points fall on two clearly separated straight lines. A similar correlation is found for a plot of ΔΔG* per D atom vs. ΔΔH* per D atom.The significance of the correlation is discussed and a possible rationalization, in terms of mechanism and particularly the role of the solvent is given.