Computational study of hexanal peroxy radical–water complexes

The results of an ab initio study on a family of hydroxy peroxy radical–water complexes formed from the oxidation of E‐2‐hexenal, which constitutes an important component of biogenic atmospheric emissions, are reported. Binding energies for the β‐hydroxy‐γ‐peroxy hexanal (β‐ and γ‐positions are relative to the carbonyl) radical–water complex and the γ‐hydroxy‐β‐peroxy hexanal radical–water complex are predicted to be to 3.8 and 3.6 kcal/mol, respectively, computed at the MP2/6‐311++G(2d,2p)//B3LYP/6‐311++G(2d,2p) computational level. Natural bond orbital reveals that conventional hydrogen bonding between the water and the hydroxy and aldehyde functional groups of the radical are primarily responsible for the stability of the complex. It can be shown that the peroxy moiety contributes very little to the stability of the radical–water complexes. Thermochemistry calculations reveal estimated equilibrium constants that are comparable to those recently reported for several hydroxy isoprene radical–water complexes. The results of this report suggest that the hexanal peroxy radical–water complexes are expected to play a significant role in the complex chemistry of the atmosphere. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011