Intrinsic barrier for protonation of radical anions

Ab initio calculations on radical anions show that, counterintuitively, protonation on the radicaloid carbon is favored. In the case of radical anions derived from acrylonitrile and acrylaldehyde, protonation on the heteroatom is less favored than protonation on the radicaloid carbon. However, in nitroethylene, the preferred protonation site is on the nitro oxygen in accordance with experimental observation.