Communication: Energetics of reaction pathways for reactions of ethenol with the hydroxyl radical: The importance of internal hydrogen bonding at the transition state

We find high multireference character for abstraction of H from the OH group of ethenol (also called vinyl alcohol); therefore we adopt a multireference approach to calculate barrier heights for the various possible reaction channels of OH+C2H3OH. The relative barrier heights of ten possible saddle points for reaction of OH with ethenol are predicted by multireference Møller–Plesset perturbation theory with active spaces based on correlated participating orbitals (CPOs) and CPO plus a correlated π orbital (CPO+π). Six barrier heights for abstracting H from a CH bond range from 3.1 to 7.7 kcal/mol, two barrier heights for abstracting H from an OH bond are both 6.0 kcal/mol, and two barrier heights for OH addition to the double bond are −1.8 and −2.8 kcal/mol. Thus we expect abstraction at high-temperature and addition at low temperature. The factor that determines which H is most favorable to abstract is an internal hydrogen bond that constitutes part of a six-membered ring at one of the abstraction saddle points; the hydrogen bond contributes about 3 kcal/mol stabilization.