Formaldehyde mediated proton-transport catalysis in the ketene-water radical cation CH2{double bond, long}C({double bond, long}O)OH2{radical dot}+

Previous studies have shown that the solitary ketene-water ion CH2{double bond, long}C({double bond, long}O)OH2{radical dot}+ (1) does not isomerize into CH2{double bond, long}C(OH)2{radical dot}+ (2), its more stable hydrogen shift isomer. Tandem mass spectrometry based collision experiments reveal that this isomerization does take place in the CH2{double bond, long}O loss from low-energy 1,3-dihydroxyacetone ions (HOCH2)2C{double bond, long}O{radical dot}+. A mechanistic analysis using the CBS-QB3 model chemistry shows that such molecular ions rearrange into hydrogen-bridged radical cations [CH2C({double bond, long}O)O(H)-H⋯OCH2]{radical dot}+ 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.

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