[Rosalind Franklin]

Hello!

I was trying out this problem and I have tried to arrange the three structures in decreasing order of stability. Structure 1 is the most stable because it's aromatic, has inductive and hyperconjugation effects stabilizing the carbocation as well. Structure 3 is the least stable but I am not able to come up with a logical reason as to why that is so. Structure 2 has one resonance structure. Could Structure 2 be more stable than 3 because of that? Aren't both carbons in structure 2 and 3 having + charge sp2 hybridised? What am I missing here?

[mjc123]

Maybe if you draw in the hydrogens it would help clarify the difference between 2 and 3.

[Rosalind Franklin]

Maybe if you draw in the hydrogens it would help clarify the difference between 2 and 3.

Carbocation in structure 3 is sp hybridized not sp2. And a positive charge on sp is less stable. Got it. I will remember to draw the hydrogens next time. Thank you very much.