Reactivity at the Phenylmethyl Benzyl Carbon Benzylic Resonance Stabilization

REACTIVITY AT THE PHENYLMETHYL (BENZYL) CARBON BENZYLIC RESONANCE STABILIZATION 

Benzylic radicals are reactive intermediates in the halogenation of alkylbenzenes 

We have seen that benzene will not react with chlorine or bromine unless a Lewis acid is added. The acid catalyzes halogenation of the ring (Section 15-9). 

In contrast, heat or light allows attack by chlorine or bromine on methylbenzene (toluene) even in the absence of a catalyst. Analysis of the products shows that reaction takes place at the methyl group, not at the aromatic ring, and that excess halogen leads to multiple substitution. 

Each substitution yields one molecule of hydrogen halide as a by-product. 

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