2.3- Dimethylbutane, photochlorination

Branching. Photochlorination of 2,3-dimethylbutane in the liquid phase leads to a mixture of I and II.42... 

The 2-chloro/l-chloro ratio in chlorination of 2,3-dimethylbutane, for instance, is 12.0 with sulfuryl chloride versus 4.2 in photochlorination. The chlorosulfonyl radical, however, easily decomposes under reaction conditions to yield a chlorine atom [Eq. (10.19)], which also participates in chlorination ... 

The variation in selectivity of radicals in different solvents has been interpreted as being due to radical-solvent interaction which changes the reactivity of the radical. Thus the selectivity of chlorination of 2,3-dimethylbutane which may react at either a tertiary or a primary position increases in aromatic solvents (Table 26 Russell, 1958, 1960). Since the effect appears to be proportional to the basicity of the aromatic substrate, it was concluded that aromatic solvents yield a complexed chlorine atom which is consequently less reactive and therefore more selective in its reactions. Confirmation of this came from the finding that the increased selectivity of the photochlorination of 2,5-dimethylhexane in aromatic solvents was due to an increase in the activation energy of the reaction (Russell,... 

Another example of a solvent-dependent atom-transfer reaction is hydrogen abstraction by chlorine atoms during the photochemical chlorination of hydrocarbons with molecular chlorine for an excellent review, see reference [571]. Russel reported that in the photochlorination of 2,3-dimethylbutane, according to reaction scheme (5-68), certain solvents do not have any effect on the selectivity of the reaction as measured by the rate ratio whereas other solvents increase this ratio significantly (c/. 

In 1957, Russell et al.49-sl also demonstrated that the distribution of the products obtained in the photochlorination of 2,3-dimethylbutane in aliphatic solvents differed from that in aromatic solvents and that this difference was attributed to the... 

There is certainly strong experimental evidence for the existence of radical-solvent complexes. For instance, Russell and co-workers collected experimental evidence for radical-complex formation in studies of the photochlorination of 2,3-dimethylbutane in various solvents. In this work, different products were obtained in aliphatic and aromatic solvents, and this was attributed to formation of a Jl-complex between the Cl atom and the aromatic solvent. Complex formation was confirmed by flash photolysis. Complex formation was also proposed to explain experimental results for the addition of trichloromethane radical to 3-phenylpropene and to 4-phenyl-1-butene and for hydrogen abstraction of the t-butoxy radical from 2,3-dimethylbutane. Furthermore, complexes between nitroxide radicals and a large number of aromatic solvents have been detected. " Evidence for complexes between polymer radicals and solvent molecules was collected by Hatada et al., in an analysis of initiator fragments from the polymerization of MMA-d with AIBN and BPO initiators. They discovered that the ratio of disproportionation to combination depended on the solvent, and interpreted this as evidence for the formation of a polymer radical-solvent complex that suppresses the disproportionation reaction. 

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