Kinetic and product studies of the reactions of NO with a series of unsaturated organic compounds.

Rate coefficients for the reaction of NO radicals with 6 unsaturated volatile organic compounds (VOCs) in a 7300 L simulation chamber at ambient temperature and pressure have been determined by the relative rate method. The resulting rate coefficients were determined for isoprene, 2-carene, 3-carene, methyl vinyl ketone (MVK), methacrolein (MACR) and crotonaldehyde (CA), as (6.6 ± 0.8) × 10, (1.8 ± 0.6) × 10, (8.7 ± 0.5) × 10, (1.24 ± 1.04) × 10, (3.3 ± 0.9) × 10 and (5.7 ± 1.2) × 10 cm/(molecule•sec), respectively. The experiments indicate that NO radical reactions with all the studied unsaturated VOCs proceed through addition to the olefinic bond, however, it indicates that the introduction of a carbonyl group into unsaturated VOCs can deactivate the neighboring olefinic bond towards reaction with the NO radical, which is to be expected since the presence of these electron-withdrawing substituents will reduce the electron density in the π orbitals of the alkenes, and will therefore reduce the rate coefficient of these electrophilic addition reactions. In addition, we investigated the product formation from the reactions of 2-carene and 3-carene with the NO radical. Qualitative identification of an epoxide (CHOH), caronaldehyde (CHOH) and nitrooxy-ketone (CHONH) was achieved using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and a reaction mechanism is proposed.