Calculations predict a large inverse H/D kinetic isotope effect on the rate of tunneling in the ring opening of cyclopropylcarbinyl radical.

B3LYP/6-31G* calculations have been performed, to compute the kinetic isotope effects (KIEs) on the rate of ring opening of cyclopropylcarbinyl radical (1) to 3-buten-1-yl radical (2) at 20 K by tunneling. The most striking result of our small curvature tunneling calculations is the prediction of a 2.7-fold increase in the rate of reaction by substitution of D(2) for H(2) at C(1). The origin of this very surprising, inverse KIE on the rate of tunneling is discussed.