Solvolysis of 2-Aryl-3,3-dimethyl-2-butyl p-Nitrobenzoates. β-Deuterium Kinetic Isotope Effects and the Linear Free Energy Relationships

Article abstract of DOI:10.1016/S0040-4020(01)85982-2

Solvolysis of 2-aryl-3,3-dimethyl-2-butyl p-nitrobenzoates (4a-4d) and the 1,1,1-trideuterio derivatives (5a,5b,5c) in HFIP exhibited a high kinetic isotope effect, k(CH3)/k(CD3) = 1.90 at 60 deg C for the deactivating substrates 4c vs 5c.This effect decreased significantly with increasing electron releasing of the substituent on the aryl ring.Hammett-Brown treatment of the rate data for 4 yielded excellent linear relationships (r = 0.999) with ρ⁺ = -3.48.It is evident that the contribution of the α-methyl group to the stabilization of the cationic transition state is not constant.The approximation in the linear free energy relationship is discussed.