Investigation of the mechanism of ozonolysis of (Z)-3-methyl-2-pentene using matrix isolation infrared spectroscopy

The matrix isolation technique, combined with infrared spectroscopy and twin jet codeposition, has been used to characterize intermediates and stable “late” products formed during the ozonolysis of (Z)-3-methyl-2-pentene (MP). While twin jet deposition led to minimal product formation, annealing to 35 K produced a number of product bands. Based on isotopic labeling and theoretical calculations, product bands have been assigned to the primary ozonide and also tentatively to the secondary ozonide of MP. Indirect evidence for formation of one or both possible Criegee intermediates in this system is presented. While neither possible Criegee intermediate for this system was observed, the evidence overall clearly supports the mechanism first proposed by Criegee for the ozonolysis of alkenes. UV irradiation led to product arising from O atom addition to MP, while merged jet codeposition led to a number of stable products for this system.

► Criegee mechanism of ozonolysis of (Z)-3-methyl-2-pentene verified by spectroscopy.
► Eight fundamental vibrations of the cis-isomer of the primary ozonide of this alkene observed for the first time.
► Photochemical oxidation of this alkene by O atom addition observed.
► “Late” reaction products observed in flow reactor deposition.