(v) Isotope effects are predicted to be significant for exchanging the protium atoms of the glycyl radical, resulting in an easier H/D exchange process at Gly of the protium by deuterium than vice versa. Combining these calculations with those on the enantioselectivity of the reaction we predicted that BSS should have a low, but detectable isotope exchange activity with the product benzylsuccinate and provided an explanation for the observed H/D exchange of the glycyl radical.