Carbonyl products of the gas-phase reaction of ozone with 1-alkenes

Carbonyl products have been identified and their formation yields measured in experiments involving the gas-phase reaction of ozone with the 1-alkenes (RCH = CH2) 3-methyl-1-butene (R = i-propyl), 4-methyl-1-pentene (R = i-butyl), 3-methyl-1-pentene (R = s-butyl), 3,3-dimethyl-1-butene (R = t-butyl) and styrene (R = C6H5) at ambient T and p = 1 atm of air. Sufficient cyclohexane was added to scavenge OH in order to minimize reactions of OH with the alkenes and with their carbonyl products. Formation yields (carbonyl formed/ozone reacted) of primary carbonyls were close to the value of 1.0 that is consistent with the mechanism: O-3 + RCH = CH2 --> alpha(HCHO + RCHOO) + (1 - alpha)(H2COO + RCHO), where formaldehyde and RCHO are the primary carbonyls and H2COO and RCHOO are the biradicals. Measured sums of the primary carbonyl formation yields were 1.006 +/- 0.053 (1 S.D.) for formaldehyde + 2-methylpropanal from 3-methyl-1-butene (alpha = 0.494 +/- 0.049), 1.025 +/- 0.017 for formaldehyde + 2-methylbutanal from 3-methyl-1-pentene (alpha = 0.384 +/- 0.013), 1.147 +/- 0.050 for formaldehyde + 3-methylbutanal from 4-methyl-1-pentene (alpha = 0.384 +/- 0.020), 0.986 +/- 0.014 for formaldehyde + 2,2-dimethylpropanal from 3,3-dimethyl-1-butene (alpha = 0.320 +/- 0.012) and 0.980 +/- 0.086 for formaldehyde + benzaldehyde from styrene (alpha = 0.347 +/- 0.059). Carbonyls other than the primary carbonyls were identified; formation pathways are proposed that involve subsequent reactions of the monosubstituted biradicals RCHOO. Similarities and differences between branched-chain 1-alkenes and n-alkyl-substituted 1-alkenes are discussed. Copyright (C) 1996 Elsevier Science Ltd