Matrix Isolation Studies of Photochemical and Thermal Reactions of Cyclic Organic Substrates with Chromyl Chloride and Ozone/O Atoms

The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to characterize the products of the photochemical and thermal reactions of: i) 6-, 5-, and 3- membered rings with chromyl chloride and ii) 6-, 5-, and 3-membered rings with ozone. For the chromyl chloride systems, initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, but product bands were observed following irradiation with light of λ > 300 nm. The irradiation was shown to lead to oxygen atom transfer to the rings, forming complexes between the oxidized substrates and CrCl₂O. In all instances with a C=C bond available, a cyclic ketone complex was formed. A cyclic alcohol complex was formed depending on the electron density of the studied ring. In the saturated ring systems, a cyclic alcohol complex was formed. For the 3-membered ring, a ring-opening oxidation reaction followed by fragmentation was observed for the first time. No product bands were detected in the merged jet experiments for any of the systems, except cyclopentadiene and chromyl chloride.

For the ozone systems, initial twin jet deposition of the reagents led to visible changes in the recorded spectra of only the cyclopentadiene and cyclopentene systems (annealing led to further growth of the bands). These bands are assigned to the corresponding primary and secondary ozonides, and for the first time observed, the Criegee intermediates. Irradiation (light of λ > 200 nm) of these matrices led to the decrease in the bands and growth of new bands, producing a range of products both ring and ring-opened. Merged jet reactions for these two systems produced a large mixture of products, including ring, ring-opened, and fragmented products; no product bands were observed in any of the other systems. In all the other systems, irradiation of the matrices led to a range of ring and ring-opened products. All conclusions (both chromyl chloride and ozone systems) were supported by isotopic labeling (²H, ¹³C, ¹⁸O), by comparison to literature spectra, and by B3LYP/6-311G++(d,2p) density functional calculations.