In the above reaction, left hand side and right hand side rings are named as ' A ' and 'B' respectively. They undergo ring expansion. The correct statement for this process is:

Finally both rings will become six membered each.

Ring expansion can go upto seven membered rings

Finally both rings will become five membered each.

Hydrocarbons PYQ — JEE Main 2023 · 13 Apr · Shift 1 · Q11 with Solution

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Correct answer: A

Concept involved: ring expansion in carbocation rearrangement

Ring expansion generally occurs when a strained smaller ring forms a carbocation adjacent to the ring. A bond migrates and the ring expands to give a more stable carbocation and a less strained ring.
Usual tendency of cyclic systems
- 3-membered and 4-membered rings are highly strained.
- They readily undergo ring expansion.
- Expansion usually continues until a 5-membered or 6-membered ring is formed, because these are much more stable.
- Among these, 6-membered rings are especially stable due to very low ring strain.
About further expansion

The statement "ring expansion can go upto seven membered rings" is not generally the preferred outcome in such standard rearrangements. Expansion beyond 6-membered rings is not usually favored unless there is some special driving force.
Inference for rings A and B

Since the question says both left-hand side ring $A$ and right-hand side ring $B$ undergo ring expansion, the stable final outcome is that both rearrange to six-membered rings.
Check options
- A: Finally both rings will become six membered each. ✅
- B: Only $A$ will become 6 membered. ❌
- C: Ring expansion can go upto seven membered rings. ❌
- D: Finally both rings will become five membered each. ❌

Therefore, the correct option is:

$\boxed{A}$

View written solutionFree

Correct answer: A

Concept involved: ring expansion in carbocation rearrangement

Ring expansion generally occurs when a strained smaller ring forms a carbocation adjacent to the ring. A bond migrates and the ring expands to give a more stable carbocation and a less strained ring.
Usual tendency of cyclic systems
- 3-membered and 4-membered rings are highly strained.
- They readily undergo ring expansion.
- Expansion usually continues until a 5-membered or 6-membered ring is formed, because these are much more stable.
- Among these, 6-membered rings are especially stable due to very low ring strain.
About further expansion

The statement "ring expansion can go upto seven membered rings" is not generally the preferred outcome in such standard rearrangements. Expansion beyond 6-membered rings is not usually favored unless there is some special driving force.
Inference for rings A and B

Since the question says both left-hand side ring $A$ and right-hand side ring $B$ undergo ring expansion, the stable final outcome is that both rearrange to six-membered rings.
Check options
- A: Finally both rings will become six membered each. ✅
- B: Only $A$ will become 6 membered. ❌
- C: Ring expansion can go upto seven membered rings. ❌
- D: Finally both rings will become five membered each. ❌

Therefore, the correct option is:

$\boxed{A}$