Photodimerizations

Surfactants have also been of interest for their ability to support reactions in normally inhospitable environments. Reactions such as hydrolysis, aminolysis, solvolysis, and, in inorganic chemistry, of aquation of complex ions, may be retarded, accelerated, or differently sensitive to catalysts relative to the behavior in ordinary solutions (see Refs. 205 and 206 for reviews). The acid-base chemistry in micellar solutions has been investigated by Drummond and co-workers [207]. A useful model has been the pseudophase model [206-209] in which reactants are either in solution or solubilized in micelles and partition between the two as though two distinct phases were involved. In inverse micelles in nonpolar media, water is concentrated in the micellar core and reactions in the micelle may be greatly accelerated [206, 210]. The confining environment of a solubilized reactant may lead to stereochemical consequences as in photodimerization reactions in micelles [211] or vesicles [212] or in the generation of radical pairs [213]. 

The C-C linkage in tire polymeric [60]fullerene composite is highly unstable and, in turn, tire reversible [2+2] phototransfonnation leads to an almost quantitative recovery of tire crystalline fullerene. In contrast tire similarly conducted illumination of [70]fullerene films results in an irreversible and randomly occurring photodimerization. The important aspect which underlines tire markedly different reactivity of tire [60]fullerene polymer material relative to, for example, tire analogous [36]fullerene composites, is tire reversible transfomration of tire fomrer back to the initial fee phase. 

Wang Y, Hoiden J M, Dong Z H, Bi X X and Ekiund P C 1993 Photodimerization kinetios in soiid Cgg fiims Chem. Phys. Lett. 211 341-5... 

The role of rose bengal and other sensitizer dyes in the photodimerization of 2-acet5i-l,4-benzoquinone [1125-55-9] involves electron transfer but not singlet oxygen (42) (see Dyes, SENSITIZING). 

Fig. 7. Photodimerization of light-sensitive functional groups attached to polymer backbone stmctuies (a) polymer containing photosensitive cinnamic...

Dimerization. A coumarin dimer is formed by prolonged exposure of coumarin to sunlight or uv radiation. Photodimerization is also catalyzed by boron trifluoride (30). 

Photosensitized Reactions for Polymers. The economic and technical features for photocross-linking, photosolubilizafion, and photopolymerization reactions have been reviewed (55). The widely used poly(vinyl ciunamates) (PVCN) photocross-link by a photodimerization reaction. 

Unusual heterocyclic systems can be obtained by photodimerizations and for five-membered heterocycles with two or more heteroatoms such dimerizations need be effected on their ring-fused derivatives. Cyclobutanes are usually obtained as in the photodimerization of the s-triazolo[4,3-a]pyridine (540) to the head-to-head dimer (541). These thermally labile photodimers were formed by dimerization of the 5,6-double bond in one molecule with the 7,8-double bond in another (77T1247). Irradiation of the bis( 1,2,4-triazolo[4,3-a]pyridyl)ethane (542) at 300 nm gave the CK0ifused cyclobutane dimer (543). At 254 nm the cage-like structure (544) was formed (77T1253). 

H-Pyran-2,6-dicarboxylic acids synthesis, 3, 758 Pyran-2,4-dione, 3,3-dimethyl-photodimerization, 3, 720 reactions... 

Pyran-4-one, 2,2,5-trimethyl-2,3-dihydro-photodimerization, 3, 720 4H-Pyran-4-one, 2,3-dihydro-2,3,5-trimethyl-6-( 1 -methyl-2-oxobutyl)-synthesis, 3, 844 Pyranones alkylation, 2, 56 aromaticity, 3, 632, 633 C NMR, 3, 587, 635 H NMR, 3, 580 cardiac glycosides, 3, 883 chromone synthesis from, 3, 830 colour couplers... 

The photodimerization of thiochromone 1,1-dioxide (67) has also been studied. In... 

An example of intramolecular abstraction has already been given (p. 318). Category 6. Photodimerization. An example is dimerization of cyclopente-... 

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