Primary alkyl radicals: Can they be persistent?

The structure of t ‐Bu 3 SiċH 2 , (I), suggested that it might be a persistent primary alkyl radical since it has (i) a bulky group to protect the radical center; (ii) no β‐hydrogens, so that a radical‐radical disproportionation reaction is impossible; (iii) a β‐silicon atom, which should prevent β‐scission of tert ‐butyl as a unimolecular decomposition pathway. However, the self‐reaction of (I) in isooctane was found to be a diffusion controlled process with log( A / M −1 sec −1 ) = 10.7 ± 0.3 and E = 2.5 ± 0.2 kcal mole −1 . Hence (I) is not persistent and it is concluded that a persistent primary alkyl will only be observed when the—ĊH 2 moiety is deeply buried among sterically protecting groups.