RATE CONSTANTS FOR THE GAS-PHASE REACTION OF OZONE WITH 1,1-DISUBSTITUTED ALKENES

The gas-phase reaction of ozone with eight alkenes including six 1,1-d isubstituted alkenes has been investigated at ambient T (285-298 K) an d p=1 atm. of air. The reaction rate constants are, in units of 10(-18 ) cm(3) molecule(-1) s(-1), 9.50+/-1.23 for 3-methyl-1-butene, 13.1+/- 1.8 for 2-methyl-1-pentene, 11.3+/-3.2 for 2-methyl-1.3-butadiene (iso prene), 7.75+/-1.08 for 2,3,3-trimethyl-1-butene, 3.02+/-0.52 for 3-me thyl-2-isopropyl-1-butene, 3.98+/-0.43 for 3,4-diethyl-2-hexene, 139+/ -17 for 2,4,4-trimethyl-2-pentene, and >370 for (cis+trans)-3,4-dimeth yl-3-hexene. For isoprene, results From this study and earlier literat ure data are consistent with: k (cm(3) molecule(-1) s(-1))=5.59 (+3.51 , -2.16)x10(-15) e((-3606+/-279/RT)), n=28, and R=0.930. The reactivit y of the other alkenes, six of which have not been studied before, is discussed in terms of alkyl substituent inductive and steric effects. For alkenes (except 1,1-disubstituted alkenes) that bear H, CH3, and C 2H5 substituents, reactivity towards ozone is related to the alkene io nization potential: In k (10(-18) cm(3) molecule(-1) s(-1))=(32.89+/-1 .84)-(3.09+/-0.20) IP (eV), n=12, and R=0.979. This relationship overp redicts the reactivity of C-greater than or equal to 3 1-alkenes, of 1 ,1-disubstituted alkenes, and of alkenes with bulky substituents, for which reactivity towards ozone is lower due to substituent steric effe cts. The atmospheric persistence of the alkenes studied is briefly dis cussed. (C) 1996 John Wiley & Sons, Inc.