Collisionally activated dissociation of 1-benzyloxypyridinium cations

Abstract

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 (E_app) have been measured for both pathways; they are higher by 3–17 kcal mol^–1 for the dominant pathway (A) than for (B).

The E_app values are compared with the ΔH_f 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 E_app 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.