Explain the following reaction in mechanistic terms. Show arrow pushing. The total number of new C-C σ bonds formed when the polyene reacts with HBr to give the bicyclic bromide is :

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H + adds to the CH= carbon of the (CH 3 ) 2 C=CH end (Markovnikov), giving a tertiary carbocation. The next C=C attacks this cation (6-membered ring, 1st new C-C bond) and gives a new tertiary cation; the last C=C attacks that cation (second 6-membered ring, 2nd new C-C bond). Br - then captures the final tertiary cation. Two new C-C σ bonds, so the answer is (A).

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