Question: An allylic alcohol contains an OH group on a carbon atom adjacent to a double bond. The treatment of allylic alcohol A with HCl forms a mixture of two allylic chlorides, B and C. Draw a stepwise mechanism that illustrates how both products are formed.
The carbocation that has more hyperconjugation structures will attain more stability.
The order of stability among various carbocations is as shown below.
In the given reaction, is not a good leaving group, but when it reacts with the acid, it is converted into the better leaving group .
Thus, an allylic carbocation is formed as an intermediate and, on reaction with a chloride ion, forms the product B. The rearrangement of carbocation takes place due to resonance and this, on reaction with the chloride ion, forms product C.
The mechanism is as shown below.
Representation of the reaction mechanism
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