Norrish photoprocess

For a long time, the similarity between thermal and photolytic products was a mystery because Norrish photoprocesses are absent in the former situation. By using low MW model compounds, chemical derivatization, and C-NMR techniques, it has been assessed that a large fraction of the carbonylduring oxidative degradation of PP are a-methylated acids. Such a carboxylic structure can only originate from the oxidation of macroalkyl radicals [Eq. (51)1, which can be formed either by a Norrish I photoprocess or by j -sdssion of alkoxy radicals (Ref. 10, p. 583). 

In spite of the diversity in photoinitiation mechanisms, two principal modes of reaction can be identified in most commercial polymers the Norrish photoprocesses and the photo-Fries rearrangement. 

Scheme 15.2. Norrish photoprocesses in carbonyl-containing polymers.

In the most constraining cages of solid -nonadecane or stretched LDPE and HDPE, the ee of 2-AN is somewhat lower because of a secondary photoprocess, analogous to the first step in the Norrish-Yang reaction, that its keto precursor (Equation 13.5) under goes, (a) Mori, T. Takamoto, M. Saito, H. Euro, T. Wada, T. Inoue, Y. Chem. Lett. 2004, 33, 256. (b) Jimenez, M. C. Miranda, M. A. Scaiano, J. C. Tormos, R. Chem. Commun. 1997, 1487. 

A study of the primary photoprocesses in gaseous 1-nitropropane has been undertaken. The major product, ethylene, is believed to arise via a pathway analogous to that responsible for the Norrish Type II reaction. At higher temperatures, carbon-nitrogen bond homolysis is also observed. A curious series of transformations has been reported for 2-nitrodibenzo[6,e][l,4]dioxin (234) on C. Dupuy and J. M. Surzur, Bull. Soc. Chim. Fr., 1980, 374. 

The Norrish Type I photocleavage of the 2-(2-cyclopropylcyclopropyl)-alkanones (36) has been described.44 The many products from the reaction were reduced in number by catalytic hydrogenation to afford (37a 61%) and (38a 20%) from (36a), and (37b 51%) and (38b 24%) from (36b). Studies at low conversion of (36a) indicated that the six-atom ring-expansion was a primary photoprocess involving one photon. 

Ariel, S., Ramamurthy, V., Scheffer, J. R., and Trotter, J., The Norrish type II reaction in the sohd state involvement of a boathke reactant conformation, /. Am. Chem. Soc., 105,6959, 1983. Wagner, P. J., Kelso, P. A., Kemppainen, A. E., and Zepp, R. G., Type II photoprocesses of phenyl ketones competitive 5-hydrogen abstraction and the geometry of intramolecular hydrogen atom transfers, /. Am. Chem. Soc., 94, 7500,1972. 

---