Atmospheric Chemistry of Enols: Vinyl Alcohol + OH + O2 Reaction Revisited.

The OH-initiated oxidation of vinyl alcohol (VA) produced by phototautomerization of acetaldehyde is thought to be a source of formic acid (FA) in the atmosphere. A recent theoretical study predicted that the VA + OH + O2 reaction 1 proceeds by OH addition at α-C (66%) and β-C (33%) of VA and that FA is a main product of reaction 1. However, the metastable reactant ( anti-VA, ∼18% at 298 K, 1.42 kcal mol-1 higher than syn in energy) used in that study inspired us to reinvestigate reaction 1. Using the state-of-the-art quantum-chemical and kinetic calculations, we first found that a conformer of VA has a significant influence on the rate coefficient and branching ratio of reaction 1. Upon derivation, it is found that ∼84% of reaction 1 takes place through the β-C-addition channel and ∼16% of reaction 1 happens by the α-C-addition channel. The calculated total initial rate coefficient at 298 K is 1.48 × 10-11 cm3 molecule-1 s-1, which is in reasonable agreement with the experimental values of similar systems (vinyl ethers + OH reactions). The predicted main products of reaction 1 are glycolaldehyde and the HO2 radical, whereas FA is just a byproduct.