The gas-phase reaction of alkenes with ozone: formation yields of carbonyls from biradicals in ozone–alkene–cyclohexane experiments

Data from ozone–alkene–cyclohexane experiments are analyzed with focus on carbonyls other than the primary carbonyls R1COR2 and R3COR4. Formation of these carbonyls is consistent with O3+R1R2C=CR3R4→α(R1COR2+R3R4COO)+(1−α) (R3COR4+R1R2COO) followed by reactions of the biradicals R1R2COO and R3R4COO via an unsaturated hydroperoxide, e.g. for the biradical RCH2CHOO, (RCH2CHOO)*→(RCH=CH(OOH))*→(RCH(OH)CHO)* (1), followed by (RCH(OH) CHO)*→RCH(OH)CHO and/or H2+RC(O)CHO (2) or by (RCH(OH)CHO)*→HCO+RCHOH (3a) followed by RCHOH+O2→HO2+RCHO (3b). Formation yields of carbonyls for biradicals from 35 alkenes are presented as follows: RCHOO→A(CND)+B(MFC+CO+2HO2) and R1R2COO→A1(CND1)+A2(CND2)+B1(MFC1+HO2)+B2(MFC2+HO2), where CND are the Cn hydroxycarbonyls and/or α-dicarbonyls (reaction (2)), MFC are the monofunctional carbonyls (reaction (3)), and Cn is the number of carbon atoms in the biradical. For 12 monosubstituted biradicals RCHOO, A=0.02–0.30 (average=0.14), B=0.04–0.23 (average=0.14) and A+B=0.07–0.42 (average=0.24). For eight disubstituted biradicals R1R2COO, A=0.20–0.42 (average=0.29), B=0.25–0.58 (average 0.32) and A+B=0.48–0.86 (average >0.61). Consistent with, and supportive of, the biradical→peroxide pathway that involves H-atom abstraction (reaction (1)), no carbonyls are observed to form when R=t-butyl. Reactions 2 and 3 are of comparable magnitude, with on the average B/A=1.40 (n=16) for RCHOO and 1.13 (n=9) for R1R2COO. Values of A, B and A+B are 2–3 times higher for R1R2COO than for RCHOO. Using data for alkenes that lead to the same biradical, formation yields of primary carbonyls for eigth alkenes are corrected for the contribution of biradical reactions. Formation yields of CO and HO2, which may form in pathways other than reactions (1)–(3), are B for monosubstituted biradicals for CO, and, for HO2, B for R1R2COO and (2×B) for RCHOO. For a given alkene, the numerical value of (A+B) is a lower limit for the biradical→unsaturated hydroperoxide pathway and conversely the numerical value of (1−(A+B)) is an upper limit of all biradical reactions other than reaction (1).