Question

Question: Which alkene reacts faster with HBr? Explain your choice

Short answer

Answer

B

Step-by-step solution

Reactivity of alkene  

The reactivity of an alkene depends on resonance stabilization. If the alkene forms a resonance stabilized carbocation on reaction with HBr, it will react faster.

Explanation

Compound B reacts with HBr to give the benzyl carbocation on either side of the double bond. The benzyl carbocation is the most stable because it undergoes resonance.

Therefore, compound B reacts faster than A.

Resonance stabilization of B

Compound A reacts with HBr does not give more stable carbocation. Therefore, there is no resonance stabilization and compound A reacts slow.