Nonstereospecific Mechanisms in the Photolysis of Cyclic Ketones¹

A study of product ratios in the direct (313 nm) and Hg‐sensitized (254 nm) photodecomposition of 2‐methylcyclohexanone in the gas phase

“…A variation of the ratio with temperature is clearly seen in Table 111, with average values of 2.39 at 100°C and 1.43 at 250°C. Tables 1-111 confirm that internal hydrogen abstraction is favored over cyclization for 1,5-biradicals7 as found in other studies [4,8,10,23]. In 2,6-DMCH photolysis a temperature dependence was also seen for the 2-heptene/dmcp ratio, decreasing from 2.64 at 100" to 2.08 at 150°C [8].…”

“…Relative rates of product formation were identical with either set-up. Experiments at 19.5 torr were carried out in a conventional vacuum system [1,8]; the volume of the cylindrical quartz photolysis cell was 164 mL, and pressures were measured by a sloping mercury magnifying manometer [9]. Experiments at 5 2 .…”

“…At high conversions photolysis of the aldehydes can occur [1,8], with a slight preference for photodegradation of the cis isomer [l]. In the present work we performed some experiments with a mixture of t-A and c-A under Hg-sensitized conditions.…”

The photolysis of 2‐fluorocyclohexanone in the 313‐nm region. The elimination of hydrogen fluoride from vibrationally excited fluorocyclopentane

“…This work cyclopentene + fluorocyclopentane 1.04 f 0.13 at 18OOC). Similar effects have been observed previously [13,14, for various radicals, and a fuller account will be given for hexane-1,5-diyl [13,36].…”

Radiation and Photochemistry

“…Alumbaugh, Pritchard & Rickborn (152) reported that photolysis of either cis-or trans-2,6-dimethylcyclohexanone gave the same products in the same product ratios. They concluded that this nonstereospecificity rules out a concerted mechanism such as that proposed earlier by Srinivasan (153), and points to the formation of a diradical intermediate.…”