Homogeneous solution, photolysis

With respect to using methyl viologen as electron relay, it might be of interest to note tlmt MV " can be oxidized by positive holes produced in illuminated colloidal semiconductors such as Ti02 Two oxidation products of MV are 1, 2 -di-hydro-l,r-dimethyl-2 -oxo-4,4 -bipyridylium chloride and 3,4-dihydro-l,r-dime-thyl-3-oxo-4,4 -bipyridylium chloride, which can readily be detected by their strong fluorescences at 516 nm and 528 nm, respectively. These products are also produced in the direct photolysis of MV " solutions and in the reaction of MV "" with OH radicals in homogeneous solution... 

Sakamoto et al. also demonstrated the absolute oxetane synthesis in the solid-state photolysis of N-(a, 3-unsaturated carbonyl)benzoylformamides 39 (Scheme 18) [25]. These compounds undergo intramolecular [2 + 2] cyclization to give bicyclic oxetanes 40 in homogeneous solution. The x-ray analysis of N-isopropyl substituted imide 39a revealed that the crystal system was monoclinic and the space group P2 (Table 7). Crystals of 39a were powdered and photolyzed at 0°C. The imide undergoes the [2 + 2] cycloaddition to afford the bicyclic oxetane 40a, which is a mixture of diastereomers, namely, syn- and anti isomers at the C-7 position. In this reaction optically active syn-oxetane 40a with 37% ee (84% chemical yield) and racemic anti-40a were obtained (Table 8). The solid-state photoreaction proceeded even at — 78°C, and optically active syn-40a, which showed ee value as high as > 95% ee (conv 100%, chemical yield 89%), was... 

A minor product observed in the photolysis of DBK in aqueous HDTCl (Fig. 5) is the isomeric ketone 4-methylphenylacetophenone (PMAP, 3) 15 18). The question arises as to whether the formation of 3 is due to some special orienting feature of the micelle which operates on the ratio of coupling products 1 and 3. Although 3 has not been detected by the conventional analytical methods for product analyses, (e.g., vpc), some 3 is detectable via chemically induced dynamic nuclear polarization (CIDNP) measurements 28). Thus, it may be that the ratio of formation of 1 to 3 is similar in both micellar and homogeneous solutions, but that the absolute yield of both combination products is so much smaller in homogeneous solution that 3 is not detectable by conventional analyses. 

The photolysis of (/ )-A-10-methyl-2-octalone (125) [350] in homogeneous solution led to the formation of the products shown in Scheme 37. The II/III ratio is solvent dependent, with II favored in nonpolar media. In the a-CD solid complex, II is the major product (20 1). In the photolysis of the complex dissolved in water, a new product was isolated, corresponding to the addition of water. 

The yields of the products change upon solubilization of the reactants because of the change of the effective polarity and microviscosity of the micellar phase as compared with the bulk phase. There are reactions for which the solubilization itself changes the yields of the photoproducts due to the compartmentalization of the reactants and intermediates of the reaction. For example, the photolysis of the asymmetric ketones in homogeneous solutions results in different radicals, which form a number of products as a result of a bulk recombination [22] ... 

Kinetic and thermodynamic studies of organometallics in the gas phase have progressed steadily from systems involving highly unsaturated complexes, often with positively charged metal centers, to systems that are directly relevant to reactions in homogeneous solution. An outstanding example of this involves time-resolved IR spectroscopic studies of [W(CO)5] produced by flash photolysis of [W(CO)6] in the gas phase. Kinetic and equilibrium data for reactions (8) provide equilibrium and rate constants from 300 to... 

The nanospace of zeolite may impose a restriction on the rotational and translational motions of substrate molecules and reaction intermediates. This would promote or discourage specific reactions. The photochemical reaction of phenyl phenylacetates 1-4 (Scheme 10.25) within zeolites can be regarded as a good example [110, 111]. Photolysis of 1-4 in a homogeneous solution results in the formation of ortho-hydroxyphenones (40-60%), para-hydroxyphenones (20-25%), phenols (5-15%), diphylethanes (5-15%), and phenyl benzyl ethers (3-8%). However, the photolysis of all four esters in NaY zeolite can produce only ortho-hydroxyphenones. Molecular models suggest that the esters 16-19 can enter into... 

Another intermediate of the photolysis of TiO was observed in experiments with platinized particles (in the absence of polyvinyl alcohol). The spectrum shown in Fig. 22 is prraent immediately after the laser flash. The signal decays as shown by the inset in the figure. The rate of decay is not influenced by oxygen but is increased by oxidizable compounds such as Br ions in the solution. The broad absorption band in Fig. 22 with a maximum at 430 nm was attributed to trapped positive holes. Chemically, a trapped hole is an 0 radical anion. In homogeneous aqueous solution, 0 ... 

Lipczynska-Kochany E. Degradation of nitrobenzene and nitrophenols in homogeneous aqueous solution. Direct photolysis versus photolysis in the presence of hydrogen peroxide and the Fenton reagent. Water Pollut Res J Can 1992 27 97-122. 

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