OH-initiated degradation of a series of hexenols in the troposphere: rate coefficients at 298 K and 1 atm

Abstract

The kinetics of the reactions of OH radicals with three C6 unsaturated alcohols at 298 K and atmospheric pressure were investigated using solid phase microextraction (SPME) with GC-FID detection of organic compounds. Rate coefficients (in cm3 molecule1 s1 ) of k1(OH þ (E)-CH2OHCH] CH(CH2)2CH3) ¼ (1.0 0.3) 1010, k2(OH þ (E)-CH2OHCH2CH]CHCH2CH3) ¼ (1.2 0.2) 1010 and k3(OH þ (Z)-CH2OHCH2CH]CHCH2CH3) ¼ (1.4 0.3) 1010 were obtained by the relative rate method using methyl methacrylate and (E)-2-buten-1-ol as references. Rate coefficients were compared with previous determinations and reactivity trends were developed and rationalized in terms of the effect and position of substituents in the unsaturated alcohol. A correlation between the reactivity of unsaturated alcohols toward OH radicals and the energy of the HOMO of the unsaturated alcohol is presented. Additionally, product identification under atmospheric conditions was performed for the first time for these unsaturated C6 alcohols by the GCeMS technique. Butanal was observed as the main degradation product of OH with (E)-2-hexen-1-ol, in accordance with the decomposition of the 2,3-hydroxyalcoxy radicals formed. On the basis of our kinetic measurements, tropospheric lifetimes of the studied unsaturated compounds are estimated.