Surprising Stability of Larger Criegee Intermediates on Aqueous Interfaces

Criegee intermediates have implications as key intermediates in atmospheric, organic, and enzymatic reactions. However, their chemistry in aqueous environments is relatively unexplored. Herein, Born–Oppenheimer molecular dynamics (BOMD) simulations examine the dynamic behavior of syn- and anti-CH₃CHOO at the air–water interface. They show that unlike the simplest Criegee intermediate (CH₂OO), both syn- and anti-CH₃CHOO remain inert towards reaction with water. The unexpected high stability of C₂ Criegee intermediates is due to the presence of a hydrophobic methyl substituent on the Criegee carbon that lowers the proton transfer ability and inhibits the formation of a pre-reaction complex for the Criegee–water reaction. The simulation of the larger Criegee intermediates, (CH₃)₂COO, syn- and anti-CH₂C(CH₃)C(H)OO on the water droplet surface suggests that strongly hydrophobic substituents determine the reactivity of Criegee intermediates at the air–water interface.