Kinetics and products of the reactions of oh radicals with 4,4-dimethyl-1-pentene and 3,3-dimethylbutanal at 296 +/- 2 K

Abstract

Using a relative rate method, rate constants have been measured for the reactions of OH radicals with 4,4-dimethyl-1-pentene [(CH(3))(3)CCH(2)CH=CH(2)] and its major reaction product, 3,3-dimethylbutanal [(CH(3))(3)CCH(2)CHO], at 296 +/- 2 K and atmospheric pressure of air. The rate constants obtained were 2.41 x 10(-11) and 2.73 x 10(-11) cm(3) molecule(-1) s(-1), respectively, with estimated uncertainties of +/-10%. The products identified and quantified by gas chromatography with mass spectrometry and/or flame ionization detection from the 4,4-dimethyl-1-pentene reaction were acrolein [CH(2)=CHCHO], 3,3-dimethylbutanal, and a molecular weight 112 carbonyl attributed to 4,4-dimethyl-2-pentenal [(CH(3))(3)CCH=CHCHO], with formation yields of 2.7 +/- 0.5%, 59 +/- 6%, and 3.4 +/- 0.6%, respectively. Using direct air sampling atmospheric pressure ionization mass spectrometry, additional products of molecular weight 146, 177, and 193 were observed, and on the basis of expected reaction schemes these are attributed to the dihydroxycarbonyl HOCH(2)C(CH(3))(2)CH(2)C(O)CH(2)OH, the hydroxynitrates (CH(3))(3)CCH(2)CH(OH)CH(2)ONO(2) and/or (CH(3))(3)CCH(2)CH(ONO(2))CH(2)OH, and the dihydroxynitrate O(2)NOCH(2)C(CH(3))(2)CH(2)CH(OH)CH(2)OH, respectively. The hydroxynitrates were also tentatively identified by gas chromatography, with a summed yield of approximately 15%. Acrolein and 4,4-dimethyl-2-pentenal arise from H-atom abstraction from the three equivalent CH(3) groups and the 3-position CH(2) group, and the sum of their formation yields (6.1 +/- 0.8%) is expected to be very close to the fraction of the overall reaction proceeding by H-atom abstraction.