Prodcuts and mechanism of the reaction of OH radicals with 2,3,4-trimethylpentane in the presence of NO

Alkanes are important constituents of gasoline fuel and vehicle exhaust, with branched alkanes comprising a significant fraction of the total alkanes observed in urban areas. Using a relative rate method, a rate constant for the reaction of OH radicals with 2,3,4-trimethylpentane of (6.84 +/- 0.12) x 10(-12) cm(3) molecule(-1) s(-1) at 298 +/- 2 K was measured, where the indicated error is two least-squares standard deviations and does not include the uncertainty in the rate constant for the n-octane reference compound. Products of the gas-phase reaction of OH radicals with 2,3,4-trimethylpentane in the presence of NO at 298 2 K and atmospheric pressure of air have been investigated using gas chromatography with flame ionization detection (GC-FID), combined gas chromatographymass spectrometry (GC-MS), and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). Products identified and quantified by GC-FID and GC-MS were (molar yields given in parentheses): acetalclehyde (47 +/- 6%), acetone (76 +/- 11%), 3-methyl-2-butanone (41 +/- 5%), 3-methyl-2-butyl nitrate (1.6 +/- 0.2%), and 2-propyl nitrate (6.2 +/- 0.8%). These compounds account for 69 +/- 6% of the reaction products, as carbon. Additional products observed by API-MS analyses using positive and negative ion modes were C-5- and C-8-hydroxynitrates and a C-8-hydroxycarbonyl, which, together with the predicted formation of octyl nitrates, account for some or all of the remaining products. The product distribution is compared to those for the linear and branched C-8-alkanes n-octane and 2,2,4-trimethylpentane.