Irradiation by UV light

Other investigations dealt with straight-chain molecules (oi-tricosenoic acid) in which the penultimate and final carbon atoms at the hydrophobic end are connected by a double bond [91, 92]. The material does not polymerize as rapidly as those described before when irradiated by UV light, however, but it is readily polymerized when bombarded with an electron beam. It was thus thought to be an optimal material for the fabrication of electron beam resists. 

Penicillin sulfoxides can be epimerized by heat to afford thermal equilibrium mixtures of a- and /3-sulfoxides, the position of the equilibrium depending on the C(6) side chain (Scheme 5). Deuterium incorporation studies support a sulfenic acid, e.g. (18), as the intermediate in these transformations. This mechanism is also supported by the finding that when an a-sulfoxide epimerizes to a /3-sulfoxide there is a simultaneous epimerization at C(2) (71JCS(C)3540). With irradiation by UV light it is possible to convert a more thermodynamically stable /3-sulfoxide to the a-sulfoxide (69JA1530). 

Figure 2. Gas chromatographic traces of hold eagle extract, and TCDD and hexa-CDD amended extract before and after irradiation by UV light...

Photolytic. Thin films of endosulfan on glass and irradiated by UV light k >300 nm) produced endosulfan diol with minor amounts of endosulfan ether, lactone, a-hydroxyether, and other unidentified compounds (Archer et al, 1972). When an aqueous solution containing endosulfan was photooxidized by UV light at 90-95 °C, 25, 50, and 75% degraded to carbon dioxide after 5.0, 9.5, and 31.0 h, respectively (Knoevenagel and Himmelreich, 1976). 

Photolytic. Thin films of endosulfan on glass and irradiated by UV light (X >300 nm) produced... 

Photolytic. An aqueous solution irradiated by UV light at 50 °C for 1 d resulted in a 50.51% yield of carbon dioxide (Knoevenagel and Himmelreich, 1976). Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight k = 300-450 nm) photooxidized hexane into two isomers of hexyl nitrate and peroxyacetal nitrate (Cox et al, 1980). 

Methoxychlor-DDE and p,p-dimethoxybenzophenone were formed when methoxychlor in water was irradiated by UV light (Paris and Lewis, 1973). Compounds reported from the photolysis of methoxychlor in aqueous, alcoholic solutions were p,p-dimethoxybenzophenone, p-methoxybenzoic acid, and 4-methoxyphenol (Wolfe et al., 1976). However, when methoxychlor in milk was irradiated by UV light (A. = 220 and 330 nm), 4-methoxyphenol, methoxychlor-DDE, p,p-dimethoxybenzophenone, and l,l,4,4-tetrakis(p-methoxyphenyl)-l,2,3-butatriene were formed (Li and Bradley, 1969). 

When aldicarb in acetonitrile was irradiated by UV light (X = 254 nm), methylamine, dimethyl disulfide, tetramethylsuccinonitrile, and l-(methylthio)-2,3-dicyano-2,3-dimethylbutane were produced. Minor amounts of WW-dimethylurea also formed. The same products were formed when the photolyses were carried out in the presence of acetophenone, benzophenone, or benzonitrile (Freeman and McCarthy, 1984). 

Photolytic. When aminocarb in ethanol was irradiated by UV light, extensive degradation was observed. No degradation products were identified however, two unidentified cholinesterase inhibitors were reported (Crosby et al., 1965). 

When propoxur in ethanol was irradiated by UV light, only one unidentified cholinesterase inhibitor formed. Exposure to sunlight for 3 h yielded no photodecomposition products (Crosby et ah, 1965). 

Cafionic photoinitiation is based on the ring opening of the oxirane group. The photoinitiators of practical importance belong to three main classes of compounds diazonium salts, onium (e.g., iodonium and sulfonium) salts, and organometallic complexes, which upon irradiation by UV light decompose and yield an acid catalyst. 

Problem 8.53 Explain why 1,3-butadiene and Oj do not react unless irradiated by uv light to give the 1,4-adduct... 

Martin (Ref 5) obtd an expin temp of 245° for 0,02 g of the subst which detond violently after 5 sec, but this compd could not be detond by impact. The photochemical decompn of Na, K Li azides in solns irradiated by UV light of 2537-Xwave length was studied by Bonnemay (Refs 13), For low concns the reactn was homogenous and decompn proceeded at a vel proportional to the conen, but independent of the cation. At high concns the vel of decompn was not explained by a simple law (for example Beer s Law) but showed, after an induction period, that reaction proceeded by chains which formed at the start of photolysis. Crystalline Li azide can be initiated to expln by intense electron streams but not by slow neutron bombardment (Ref 16)... 

These authors also show that irradiation by UV light strongly influences the tautomeric equilibria for oxopyridines as well as for thiopyridines and thiodiazines. More importantly, this provided a reliable method to determine the relative abundance of thiol and thione... 

Over the past few years, there has been great interest in the reactions of organometallic species with dihydrogen, H2. The product of such a reaction may take one of two forms. Usually, irradiation by UV light causes loss of a CO ligand from the metal to be replaced by two individual M-H bonds. Thus, dihydrogen is added oxidatively to the metal, the H-H bond is broken, and a classical dihydride species results. 

Upon irradiation by UV light (Xexcit = 325 nm), the metallopolymer 45 exhibits a bright green emission (Xem = 525 nm) in the solid state. In contrast, a non-emissive 2D brick-wall type coordination polymer of composition [Cu2I2(L46)2]ra 46 with rhomboid dinuclear Cu—12—Cu nodes resulted from the reaction of 2-(benzylthio)-l-thiomorpholinoethanone L46 with Cul. Compared to the short Cu-Cu distance in 45, the metal metal contacts within the rhomboids of 46 are much longer and reach 2.856(2) A. 

Another manufacturing method involves irradiation by UV light, in which acrylic-modified polyurethane resins are used. Reactive fluorinated oligomers are reviewed in Reference 36. 

In the second approach to self-assembly of polymer-silica nanocomposites, polymerizable surfactants are employed both to direct self-assembly into ordered mesophases and to serve as organic monomers which can be subsequently polymerized. For instance, Brinker et al. developed nonionic surfactants incorporating diacy-telene groups which could be polymerized upon irradiation by UV light.68 69 Similarly, poly(thiophene)70 and poly(pyrrole)71 have been successfully integrated into silica nanostructures in this manner. Importantly, this in situ polymerization produces isolated molecular wires, rather than clustered bundles of conductive polymer.70... 

Horhold found that the action spectrum of phenyl-substituted polyarylene-vinylenes shifts substantially to longer wavelengths when the photoconductor probe is simultaneously irradiated by UV light from another source31. The action spectrum of photoconductivity of the polymer subjected to UV radiation is the same as the action spectrum of photoconductivity of the cation radical of the same polymer... 

Irradiation by uv light can cause the formation of thymine dimers. Does this bring about cross-linking of complementary strands of double-helical DNA ... 

Glaze el al. reported that fulgide 35 is a highly effective photochromic compound. But when the R is hydrogen atom 37a, no photocyclization reaction occurs,41 and only E —> Z photoisomerization takes place when 37a is irradiated by UV light, as shown in Scheme 8. 

Data is also shown for bovine rhodopsin, 63, for comparison. The hydroretinals 66-68 presumably assume 9-cis or 11 -cis like conformations when bound to opsin. Retinals 67 and 68 form non-bleachable pigments, i.e., no change in their A, occurs upon exposure to room light irradiation by UV light leads to decomposition products instead of separation of the chromophore from opsin. a In MeOH. In case of split chromophores the absorption maxima of the enal moieties are given. b Protonated Schiff base with n-butylamine in MeOH. ... 

In order to investigate the primary processes responsible for photocatalytic reactions Moesta and Breuer (1968) performed experiments in which simple gases, some examples of which are given later, were adsorbed on clean metal surfaces and subsequently irradiated by UV light. The different metals used in these experiments certainly do not resemble the chemical and physical composition of interstellar dust grains, but they at least offer well defined surfaces and thus avoid introducing errors due to impurities which may lead to a misunderstanding of the primary processes. 

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