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 C7H 7+ 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 Me 2NC5H4NO+. and (D) the 4-dimethylaminopyridine radical cation.