Cycloheptanone, photolysis

The products of the photolysis of cycloheptanone are carbon monoxide, propylene, a hydrocarbon fraction of the molecular formula C Hu (l),and 6-heptenal (31). The hydrocarbon fraction consists of 1-hexene and cyclohexane in the ratio of 1 4.7. A trace of ethylene has also been observed among the products. From a consideration of mass balance, the following reactions may represent the stoichiometry of the photolysis. 

The diradical mechanism as applied to this system is as hypothetical as in the cases of cyclopentanone and cyclohexanone. The only data on the use of radical scavengers is a report on the photolysis of cycloheptanone in the presence of 3.2 mm. of oxygen. In this case, both of the C hydrocarbons and 6-heptenal was observed to be formed. It is quite likely that the reactions 30-33 are concerted processes. 

Reaction I (in a peculiar form), as well as reactions II, III and IV all occur in the photolysis of cyclobutanone, though the quantum yield of step IV is very low. The occurrence of reaction III in the photolysis of cyclopentanone was not reported however, in that of cyclohexanone and cycloheptanone again all four reactions seemed to take place. 

Photochemical Reactions. Photolysis of (49) gives a low yield of 4-methylene-cycloheptanone and photolysis of (50a) and its cis-isomer in the presence of a reducing solvent gives (50b) the mechanism of the latter reaction has been studied by deuterium-labelling. The reducing solvent is needed even though a net reduction has not occurred. 

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