Role of Hydrogen-Bonded Intermediates in the Bimolecular Reactions of the Hydroxyl Radical

Because of their importance in atmospheric and combustion chemistry, the rate coefficients and mechanisms of gas-phase reactions of the OH radical have been studied extensively, and the kinetic database for these reactions is unsurpassed. The OH radical has a rather large electric dipole moment (1.668 D) and is clearly capable of forming strong hydrogen bonds. In this article, we examine the evidence for the importance of such interactions in reactions of OH. We propose that the reactions of OH with alkanes and with HNO3 represent extremes of behavior, with no effect of hydrogen bonding in the first case but reaction via a rather strongly bound intermediate complex in the second. From this base, we go on to discuss, in turn, the reactions of OH with carboxylic acids, aldehydes, ketones, hydrogen halides, and CO, with the emphasis on the possible role of hydrogen bonding between the reagents of these reactions.