The Effects of Deuterium Substitution on the Rates of Organic Reactions. VI. Secondary Isotope Effects on the Solvolysis Rates of γ-Methyl Substituted t-Alkyl Chlorides1

Abstract

Deuterium substitution beta to the chlorine of tertiary alkyl chlorides has previously been observed to have a marked decelerating influence on the rate of solvolysis of the alkyl chloride. A continuation is given of the study of these secondary isotope rate effects with particular reference to the influence of alkyl substitution on them. The 3,3-dideuterio analogs of all and the 1,1,1-trideuterio analogs of all but the second member of the following series of compounds were synthesized, and their solvolysis rates in 80% aqueous alcohol at 25 degrees measured: 2-chloro2-methylbutane, 2-chloro-2-methylpentane, 2- chloro-2,4dimethylpentane, and 2-chloro-2,4,4-trimethylpentane. The secondary isotope rate effects of the 1-deuterio substitution do not show large variations in the series while the effects of 3-deuterio substitution are about the same for all but the last member of the series where only a small effect is evident. This result is thought to be caused by steric inhibition of hyperconjugation in the neopentyl group of the last compound. Finally, the rate constants were calculated by a statistical method programmed for an electronic computer.