Rearrangements of Carbon Radicals

The rearrangement that we have already noted of carbon free radicals in the gas phase also occurs with the more complicated radicals that can be generated in the liquid phase. 

When an alkyl halide is treated with phenylmagnesium bromide in the presence of cobaltous chloride, the products obtained are partly those to be expected from unrearranged alkyl radicals and partly from rearranged ones.80 

In similar experiments in which an ethyl group was used in place of the para-tolyl group of compound V there was no rearrangement. Apparently aromatic but not aliphatic groups will migrate under these mild conditions. The same results have been obtained in experiments in which the radical is formed by a different method  

Thus the average lifetime of the neophyll radical depends on the probability of encountering an aldehyde molecule and hence on the aldehyde concentration. At high aldehyde concentrations the radical is removed by reaction (3) before it has an opportunity to rearrange. This would not be the case if rearrangement were simultaneous with formation of the radical. 

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