Formaldehyde mediated proton-transport catalysis in the ketene-water radical cation CH2C(O)OH2+

A mechanistic analysis using the CBS-QB3 model chemistry shows that such molecular ions rearrange into hydrogen-bridged radical cations [CH2C(O)O(H)-H⋯OCH2]+ in which the CH2O molecule catalyzes the transformation 1 → 2 prior to dissociation. The barrier for the unassisted reaction, 29 kcal mol−1, is reduced to a mere 0.6 kcal mol−1 for the catalysed transformation. Formaldehyde is an efficient catalyst because its proton affinity meets the criterion for facile proton-transport catalysis.