Formaldehyde mediated proton-transport catalysis in the ketene–water radical cation CH 2[dbnd]C( [dbnd]O)OH 2[rad

Abstract

Previous studies have shown that the solitary ketene–water ion CH 2 C( O)OH 2 + ( 1) does not isomerize into CH 2 C(OH) 2 + ( 2), its more stable hydrogen shift isomer. Tandem mass spectrometry based collision experiments reveal that this isomerization does take place in the CH 2 O loss from low- energy 1,3-dihydroxyacetone ions (HOCH 2) 2C O +. A mechanistic analysis using the CBS-QB3 model chemistry shows that such molecular ions rearrange into hydrogen-bridged radical cations [CH 2C( O)O(H)–H⋯OCH 2] + in which the CH 2O 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.