Consider the following molecule (X). The major product formed when X reacts with HBr (Markovnikov addition) is:
(A)(see structure)
(B)(see structure)✓ Correct
(C)(see structure)
(D)(see structure)
Answer: (B)
Solution
The polycyclic triene adds hydrogen bromide, and the proton adds to a double bond in the way that produces the most stable carbocation. Protonation at a ring-junction double bond places the positive charge on a tertiary carbon at the fusion of the rings, the most stabilised intermediate available. Bromide then bonds to this tertiary carbon, so in the major product the bromine sits on the ring-fusion carbon that bears no hydrogen, while one carbon−carbon double bond is retained on each of the other rings. The major product is the tertiary bromide carrying bromine at the ring-junction carbon.
JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Single correct option
