Photochemical generation

C—N bond homolysis may be the initial step in the conversion of (396) into the phenylazopyrazole (402), a product which is believed to arise by interaction of ground-state pyrazole with a photochemically generated phenyldiazonium ion (76CC685). 

The question of the fate of chlorofluorocarbons upon their release into the atmosphere IS of great interest at present because of the potential damage to the earth s protective ozone layer caused by the reaction of ozone with photochemically generated chlorine atoms... 

Electrochemically generated trifluoromethyl radicals add to 1-hexyne to give a 1 4 mixture of ( )- and (Z)-l,l,l-trifluoro-2-heptene [22] Kinetic data on the addition of photochemically generated trifluoromethyl radicals to acetylene and substituted acetylenes were reported [2J]. Alcohols and aldehydes add to hexa-fluoro-2-butyne in the presence of peroxide and y-ray initiation [24] (equations 16 and 17). 

Scheme 10.1 Thetmal or photochemical generation of a nitroso compound...

When these polymers are subjected to light of A = 365 nm in bulk vinyl monomer, (MMA or styrene) grafted or extensive crosslinking polymers were produced. The photografting or photocrosslinking occurs through the macro-radicals photochemically generated on the backbone of the polymer ... 

The intramolecular Diels-Alder reactions of photochemically generated trans-cycloalk-enones [162]... 

In cases where hydrogen atom transfer gives primarily reduced products, Bu3Sn-SnBu3 under photochemical generates the radical that can cyclize, but a halogen atom transfer agent such as iodoethane is usually present (see 15-44). 

Phosphonate ester (10) is made from chloride (12) available by direct chlorination with photochemical generation of radicals. 

Photochemical irradiation of dimethyl and diethyl sulphoxides yields the corresponding sulphone in the presence of air and a photosensitizer such as methylene blue in yields up to 99% . Sulphoxides are also oxidized when they act as traps for persulphoxides, the intermediate formed on reaction of a sulphide with photochemically generated singlet oxygen - , equation (9). Isotope studies have shown that such reactions proceed through a linear sulphurane intermediate . Persulphones also react with sulphoxides in a similar manner , equation (10). 

Nakatani, K. Higashida, N. Saito, I. Highly efhcient photochemical generation of o-quinone methide from Mannich bases of phenol derivatives. Tetrahedron Lett. 1997, 38, 5005-5008. 

In recent years considerable research has been done on the photochemistry and thermal chemistry of main group element azides,37 especially those of silicon. Monoazidosilanes have long been employed in the photochemical generation of iminosilanes.38,39 These products arise from the thermal or photochemical loss of molecular nitrogen accompanied by a 1,2-shift of a substituent from silicon to nitrogen. 

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