Radical photochemistry behavior

Compounds with two or more silicon atoms directly attached to one another, subdivided into sections based first on the number of silicon atoms and then on the carbon functionality attached to the silicon atoms. Frequently, but not exclusively, the main photochemical behavior involves homolysis of a silicon-silicon bond yielding silyl radicals, but in some cases silylenes result directly from the photochemistry. The resulting compounds are frequently the products of a molecular rearrangement. 

The first two derivatives in the series, monuron and metobromuron, are related to the 4-haloanilines. Their primary photochemistry has been studied by Boulkamh and Richard by means of nanosecond absorption spectroscopy [80]. The transients detected from both compounds in aqueous solution could be assigned to the N-substituted 4-iminocarbene, imino-p-benzoquinone-O-oxide and anilino radical from a complete analogy of their spectral and reactive behavior with that of the species obtained from 4-chloroaniline [55,57]. The quantum yields of carbene formation were determined to be = 0.051 for monuron and

halogen-substituted phenylurea derivatives underwent the same heterolytic dehalogenation process as the 4-haloanilines, which could be understood with reference to the protonability of the amine nitrogen, as in the case of 4-chloro-N,N-dimethylanilinc [55]. 

The photochemistry of the dimer of the triphenylimidazolyl radical is an example of photochromism whose dynamic behavior resembles that of a bistable ABC system. It is characterized by the formation of colored, relatively persistent radicals (TPI, 5). 

Similar behavior is observed in the photochemistry of water at 1849 A., where water yields H and OH radicals (65). The dependence of the... 

The reactions of n,n triplet-excited ketones are classics in photochemistry and have contributed much to the definition of molecular organic photochemistry as a field of its own [13]. For example, it took 60 years to realize that it is the triplet state of benzophenone [6] that is responsible for its photoreduction, one of the first described photoreactions [3]. With the further development of molecular organic photochemistry, the dependence of photochemical reactivity on the electronic configuration of excited states has received more detailed attention. Thus, it has been recognized that n,7t -excited states behave more radical-like in their reactions than 7t,7t -excited states [13-25]. The extensively studied hydrogen abstraction reactions of triplet-excited ketones, which mimic the behavior of alkoxyl radicals [15,16,24-29], have been taken as a test case for the characteristic radical-like n,ji reactivity. 

Diethyl mesoxalate (5, Xj 3, (heptane) = 367 (24) and 372 (25)) is the only tricarbonyl compound containing ester group(s) whose photochemical behavior has been investigated. It exhibits normal ketone photochemistry. Photolyses in cyclohexane or toluene solutions at > 320 nm gave moderate yields of the addition products (7) expected from H-atom abstraction followed by radical coupling " a number of additional products were not characterized. 

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