TEMPERATURE-DEPENDENCE OF THE DEUTERIUM-ISOTOPE EFFECT IN THE DEPROTONATION OF SOME NITROALKANES BY ANIONIC BASES

The temperature dependences of rates and deuterium isotope effects were determined for the deprotonation of 1-phenyl-1-nitroethane (1), its analogue 1-d, 1-phenyl-2-nitropropane (2) and its analogue 2-d by methoxide in methanol, ethoxide in ethanol, hydroxide/methoxide in 50% (v/v) methanol-water and hydroxide in water. The isotope effects varied little with substrate or solvent-base combination. k(H)/k(D) at 30-degrees-C was between 6.0 and 7.1 in all cases. The temperature dependences varied considerably [A(aH)/A(aD)=0.14-1-35 and E(aD) - E(aH) 0-95-2.29 kcal mol-1 (1 kcal = 4.184 kJ)]. A(aH)/A(aD) was lower with 1-phenyl-1-nitroethane than with 1-phenyl-2-nitropropane, but there was no consistent variation with solvent/base.