Effect of Carbon Chain Length on Nascent Yields of Stabilized Criegee Intermediates in Ozonolysis of a Series of Terminal Alkenes

The yields of stabilized Criegee intermediates (sCIs), CH₂OO and RCHOO (C₂H₅CHOO, C₃H₇CHOO, C₄H₉CHOO, and C₅H₁₁CHOO), produced from ozonolysis of asymmetrical 1-alkenes (1-butene, 1-pentene, 1-hexene, and 1-heptene) were investigated at low pressures (5-16 Torr) using cavity ring-down spectroscopy and chemical titration with sulfur dioxide (SO₂). By extrapolating the low-pressure measurements to zero-pressure limit, nascent sCI yields were obtained. Combined with our previous studies on ethene and propene ozonolysis, the nascent sCI yields demonstrated an intriguing trend of increasing with the addition of CH₂ groups and eventually reached a plateau at around 31% for longer chain 1-alkenes. In particular, the fraction of nascent stabilized CH₂OO reached the plateau from 1-butene, indicating that CH₂OO was produced with nearly the same internal energy distribution from 1-butene to 1-heptene. The comparison between the experiments and RRKM calculations suggests that the dissociation of primary ozonide (POZ) of O₃ + ethene and propene can be treated by statistical theory, while that of O₃ + 1-butene to 1-heptene is nonstatistical and intramolecular vibrational redistribution of the initial energy on the 1,2,3-trioxolane of POZ throughout the entire molecule was incomplete on the dissociation time scale.