Reactions of alkenylbenzenes

Most of the reactions of alkenes that were discussed in Chapter 6 find a parallel in the reactions of alkenylbenzenes... 

Addition of an unsymmetrical reagent to a double bond may in general yield two different products. In our discussion of alkenes (Secs. 6.11 and 6.17), we found that usually one of the products predominates, and that we can predict which it will be in a fairly simple way in either electrophilic or free-radical addition, the first step takes place in the way that yields the more stable particle, carbonium ion in one kind of reaction, free radical in the other kind. Does this rule apply to reactions of alkenylbenzenes ... 

The side-chain double bond is more reactive than the aromatic ring toward most electrophilic reagents. Many of the reactions of alkenes that were discussed in Chapter 6 find a parallel in the reactions of alkenylbenzenes. Thus, hydrogenation and halogen addition to a side-chain double bond can be achieved while leaving the ring unchanged. 

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