2-octanone, photolysis

The photochemistry of certain A-substituted heterocycles has also been studied. As part of a continuing investigation of the photolysis of A-nitroso compounds in solution, the conversion of A-nitroso-3-azabicyclo[3.2.2]nonane (65) into the oxime (66) by photolysis in the presence of acid was reported.58 N-Nitrosopyrrolidine is similarly transformed. The mechanism of this reaction is said58 to involve elimination of NOH with the formation of an imine as intermediate, and, in fact, in the photolysis of 2-ethyl-A-nitrosopiperidine (67), the tetrahydropyridine (68) is the major product. This mechanism certainly does not operate in the photolysis of iV-nitroso-2-azacyclo-octanone, which can be rationalized on the basis of an intramolecular hydrogen transfer [Eq. (16)].59 Acyclic iV-nitrosoamides behave in a similar fashion to IV-nitrosoamines.60... 

The results of Barltrop and Coyle , on the photolysis of aliphatic ketones in solution at 3130 A, support the explanation suggested by Wagner and Hammond for the low quantum yields. The overall quantum yield for disappearance of 2-pentanone, 2-octanone and 5-methyl 2-octanone was found to increase and approach unity in hydroxylic solvents. This increase can be attributed to the solvation of the hydroxy biradical intermediate. Since, however, the solvent effect was not observed for products originating from excited singlet molecules, it is probably only the triplet state which decomposes via biradicals. 

A variety of intramolecular photoadditions have been studied. jffy-Un-saturated ketones usually undergo 1,3- and 1,2-acyl shifts on irradiation however, in the cases of 2-cyclohept-l-enylcycloheptanone (18) and 2-cyclo-oct-l-enylcyclo-octanone (19), oxetans are the major products. An oxetan (21) was also obtained from direct photolysis of ( )-retro-y-ionone (20) although in this case photoaddition of the ketone took place across the 4,5 positions. The (Z)-isomer (22) gave a cyclobutene through... 

Gas-phase photolysis of the cyclic ketones CFa-(CFj) CF,-C 0 x = 2—5) at 3130 A does not involve migration of fluorine atoms, and the products can be explained on the basis of the general Scheme 11. Reactions 1 and la are the only ones of importance for perfluorocyclopentanone and perfluorocyclohexanone (c/. photolysis of perfiuorocyclobutanone to per-fluorocyclopropane and carbon monoxide ), and reactions 3a and 3b are important only for perfluorocyclo-octanone. 

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