Photolysis solution

The dimer showed no ESR signal as a solid but when it was dissolved in pure solvent, it gave rise to a strong characterless ESR signal, which was virtually identical to that shown by the original photolysis solution. Attempts to trap the putative diradical 75 failed, but do not rule out its possible existence as an intermediate in low concentration in the system. 

Photochemical fragmentation 165 166+167 is also feasible. Isopropyl phosphate and isopropyl methyl phosphate are expectedly found after reaction of the photolysis solution with water or methanol. It would appear that 166 (and possibly also 167) can arise directly from 164 and not only by photochemical cycloreversion of 165 since 166 is formed together with 165 even at wavelengths in the range where 165 is known to be stable. 

Solution Photolysis. Solutions were prepared by dissolving the ap-propriate carbamate (la-4a) or amine in cyclohexane (spectrograde -... 

Photolysis of a frozen aqueous solution of thymine at 254 nm gives a major product with a reported quantum yield of 1-2,31 and a minor product.32 The abundance ratio of the two products is about 8. The major product is the known thymine dimer.7,10 Identity of the minor product is unknown photolysis of it in solution produces thymine and a dimeric product which chromatographs like the major product. This minor product is alkali labile. Existence of other products in the thawed photolysis solution is suggested by details of the spectrum.32... 

Photolysis solution photolysis t/2=1294 min in n-hexadecane at 1.0 m from a GE Model RS sunlamp and surface photolysis t,/2 = 560 min on a clean glass surface under the same conditions (Nestrick et al. 1980) sunlight induced photolysis t,/2 = 380 min in isooctane solution and sunlight induced solid phase t/2 = 65 h of TCDD dispersed as solid films (Buser 1988) ... 

Figure 3 shows the GC-MS analysis of the photoreaction of silacyclobutene la in a mixture of n-pentane and methanol (1 1) exposed to irradiation from a 5 W Zn lamp for 29 h in a quartz cuvette. In the gas chromatogram plot, nine main products and more than ten by-products can be detected in the photolysis solution. The TLC analysis indicated a complex mixture too. This result is not surprising, because the short-wavelength photochemistry of a silacyclobutene follows conqilicated mechanisms [2]. 

A distinct advantage of the finely divided platinum dispersions is that the photolysis solutions remain completely transparent even at high catalyst concentration. This allows a direct study of the dynamics of the reaction of MV+ with Pt particles by employing laser photolysis technique. The upper part of Fig. 7.3 shows oscilloscope traces illustrating the temporal behaviour of the characteristic MV+ absorbance at 602 nm in the absence and presence of catalyst. The upward deflection of the signal after the laser pulse is due to the formation of MV+ via the photoredox process ... 

When vinyldisilanes are photolyzed with a mercury arc, a 1,3-shift of a silyl group from silicon to the remote sp2-hybridized carbon occurs with the formation of a silene. A simple example is shown in equation 25 and similar behavior is found if the sp2-hybridized carbon next to silicon carries a variety of substituents3,42-45. The silenes formed are not stable and unless trapped by a reagent present in the photolysis solution undergo head-to-tail dimerization (by a non-photochemical process). 

In contrast, when the solvents were polar or, more precisely, when there were kinetically acidic trapping agents present in the photolysis solution, e.g. HOR, HOH, HOAc, HCN, pyrrole, malononitrile or thiophenol, etc., the products of photolysis, formed in essentially quantitative yield, were those derived by the trapping of an intermediate siloxycarbene, which appeared to have nucleophilic character101 (equation 65). 

Photolysis solution conditions were 100 mM triethanolamine, 100 mM sodium phosphate, and 1 M ethanol. 

Given the well documented role of homolytic M-M bond cleavage in photoreactions of dinuclear carbonyls, a logical hypothesis for the photofragmentations of trinuclear complexes would be to follow a similar path to give a diradical. Indeed such an intermediate is attractive in the context that the lower quantum yields could be attributed to rapid recombination of the radicals held together by the rest of the cluster. However, experiments with added chlorocarbons in Ru3(CO)i2 photolysis solutions have shown that a trappable diradical is not an intermediate in the photoreaction chemistry, but instead the intermediate formed is susceptible to trapping by two electron donors (i.e., Lewis base nucleophiles) (eq. 13) [17,20,48-50]. 

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