Collisionally activated dissociation of 1-benzyloxypyridinium cations

Eighteen pyridine-ring substituted N-benzyloxypyridinium cations all dissociate by two alternative pathways to give (A) a cation C7H7+ and the substituted pyridine 1-oxide, and (B) a cation C7H7O+ and the substituted pyridine. Appearance potentials (Eapp) have been measured for both pathways; they are higher by 3–17 kcal mol–1 for the dominant pathway (A) than for (B).The Eapp values are compared with the ΔHf values calculated by the AM1 method for reactants and products demonstrating extensive rearrangement in a product-like transition state (TS) for pathway (A) but not for (B). Both sets of Eapp correlate roughly with Σσ for the pyridine ring substituents.For the 4-dimethylamino derivatives, two additional homolytic pathways are found to give (C) a, cation Me2NC5H4NO+˙ and (D) the 4-dimethylaminopyridine radical cation.