A Nonreacting Hydroxy Group Enhances Criegee Intermediate Reactivity through Secondary Hydrogen Bonding

The reaction of stabilized Criegee intermediate CH2OO with acetone cyanohydrin, (CH3)2C(OH)CN, provides competing O–H insertion and 1,3-dipolar cycloaddition pathways at the hydroxy and nitrile groups, respectively. We used cavity ring-down spectroscopy to measure CH2OO decay rates in the presence of excess (CH3)2C(OH)CN at different concentrations, yielding a bimolecular rate coefficient of (4.1 ± 0.3) × 10–12 cm3 s–1 at 10 Torr and 294 K, nearly 2 orders of magnitude larger than those of typical CH2OO + R–CN reactions and 1 order of magnitude larger than those of CH2OO + R–OH reactions. Potential energy surface calculations at the B3LYP-D3(BJ)/aug-cc-pVTZ level identify that the lowest-energy pathway corresponds to 1,3-dipolar cycloaddition at the nitrile site, during which the adjacent hydroxy group forms an O–H···(OOCH2) hydrogen bond that decreases the transition state (TS) enthalpy by 18 kJ mol–1 (298 K). This hydrogen-bond-assisted TS stabilization enabled by favorable functional-group proximity is interpreted to drive the enhanced Criegee intermediate reactivity.