Question

The major product formed in the following reaction is 

• A. A
• B. B
• C. C
• D. D

Hint:

Cycloheptadiene rearranges via a [1,5]-sigmatropic shift upon heating to form cycloheptatriene. Such rearrangements follow Woodward–Hoffmann orbital symmetry rules for thermal reactions.

Answer 1

The Correct Option is B

Step 1: Reaction type identification.
Cycloheptadiene undergoes a [1,5]-sigmatropic hydrogen shift or thermal rearrangement when heated to high temperatures (~170°C).
This rearrangement converts the conjugated diene into a more stable conjugated triene.
Step 2: Mechanism.
At elevated temperature, the $\pi$-electrons shift, and one of the hydrogens migrates across the conjugated system via a concerted pericyclic pathway, forming a substituted cycloheptatriene.
Step 3: Product formed.
The resulting compound is **1,3,5-cycloheptatriene** (tropylium-like structure), represented by Option (C).
Step 4: Conclusion.
The major product of the thermal rearrangement is Option (C).