Q7-55E - Organic Chemistry (Mcmurry)

Question

Use Hammond’s Postulate to determine which alkene in each pair would be expected to form a carbocation faster in an electrophilic addition reaction:

Step-by-Step Solution

Answer

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Step 1: Definition of Hammond Postulate

According to the Hammond postulate, for electrophilic addition reactions of alkene, the transition state is in resemblance with the carbocation formed. Therefore, factors which stabilize the carbocation can also stabilize the transition state.

The most stable carbocation will be form faster compared to relatively less stable carbocations.

 The order of the stability of carbocations is given below.

Step 2: Protonation of the given alkene

The alkenes when protonated gives the respective carbocations.  Since a tertiary carbocation is more stable than a secondary carbocation, it will be formed faster.

Step 3: Protonation of the given alkene

 The alkenes when protonated gives the respective carbocations.   Since a tertiary carbocation is more stable than a secondary carbocation, it will be formed faster.

Step 4: Protonation of the given alkene

The alkenes when protonated gives the respective carbocations.   Since a tertiary carbocation is more stable than a secondary carbocation, it will be formed faster.