Photosensitization, mercury

Similar mercury-photosensitized alcohol dehydrodimerizations leading to glycols have been documented (Equation (17)).26... 

The mercury-photosensitized decomposition of N20 was studied first by Manning and Noyes160 and later in greater detail and more quantitatively by Cveta-novic161,162. The primary reaction step is... 

Monoisotopic mercury photosensitization shows163 that HgO is not formed in the primary quenching reaction. 

Isotopic Effects in Mercury Photosensitization (Gunning and Strausz). . ... 

Mechanism of Energy Transfer, in Mercury Photosensitization (Gunning... 

Mechanistic Organic Photochemistry, A New Approach to (Zimmerman) Mercury Photosensitization, Isotopic Effects and the Mechanism of... 

Mercury Photosensitization, Isotopic Effects and the Mechanism of Energy... 

Cvetanovic67 was concerned with oxygen atom reactions with unsaturated hydrocarbons. The oxygen atoms were obtained in his experiments by mercury-photosensitized decomposition of N20. Cvetanovi6 came to the conclusion that the reaction of oxygen atoms with ethylene proceeded essentially with scission of the hydrocarbon bond, while with higher olefins this was not observed. Corresponding oxides (epoxides) and carbonyl compounds were formed in the course of the reaction. 

Figure 6 shows the absorption curve for acetone superimposed upon the emission spectrum of a medium pressure mercury vapor lamp of the type commonly used in photochemical investigations. If the possibility of mercury photosensitization is neglected, it can be seen that the emission line in the mercury spectrum which will be most effective in photolysis is that at 3130 A., and, in fact, this line is frequently isolated by the... 

Gunning66 has shown that disproportionation takes place when CF2C1 radicals are generated by the mercury-photosensitized decomposition of CF2CI2 and in recent studies confirming his results47 it was found that the disproportionation/combination ratio was again 0.04. 

The effect of wavelength upon the relative proportion of the products is very marked. When the 2537 A. line from a low-pressure mercury arc is used, the yield of all three ethanes is drastically reduced, while the yield of both halogenated methanes is enhanced. The 1,3-dichlorohexafluoropropane can no longer be detected. This effect is unlikely to be due to alternative primary processes, such as mercury photosensitization, since it is also observed under flash photolysis conditions. As before, it is considered that the additional energy given to the radicals at shorter wavelengths, increases the rate of abstraction and decreases the rate of combination because of the third-body restriction. Some evidence for this... 

The mercury-photosensitized decomposition of ketene27 has recently been shown to yield methylene that is believed to be in a triplet state by the rule of spin conservation. 

Duncan and Cvetanovic27 studied the reaction with isobutene of methylene generated by the mercury photosensitized decomposition of CH2CO, which is believed to produce triplet methylene. Product ratios reached high-pressure limiting ratios at 200 mm. The observed yield of... 

Methylene produced by mercury photosensitized decomposition of 011200 was found to add to cfs-butene-2 to give product ratios similar to those obtained by Frey under conditions of high dilution with argon. Addition of this type of methylene to (rans-butene-2 gave similar product ratios, with the exception that the trans isomers of 1,2-dimethylcyclo-propane and pentene-2 were favored over the cis. These results were taken as proof of the nonstereospecific addition of triplet CH2 to olefins. 

Before this interpretation can be accepted, however, direct mercury-photosensitized cis-lrans isomerization of the products would have to be ruled out. 

D. Mercury photosensitized reations. Mercury atoms are frequently used as photosensitizers in vapour phase reactions. The mechanisms involved are... 

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