Decreasing Order of Stability in unsaturated 6C Rings

[AGNuke]

Decreasing Stability order of given I, II, III, IV (in order)

A)IV>I>II>III
B)I>IV>III>II
C)I>II>IV>III
D)IV>II>I>III (My Answer)

Since the IV is most stable, only A and D answers are worth checking. They only differ by stability order of I and II.

Then I checked by determining their stability due to hyperconjugation. I has HC³ while II has HC⁴, hence my answer D. But the correct answer is A. Any suggestions, whether my answer or provided answer is correct?

 

[chemisttree]

I think it's A). Exocyclic double bonds are less stable than internal double bonds for 6-member rings but exocyclic double bonds are more stable than internal double bonds for 5-member rings.

Have you heard of Brown's Hypothesis?

 

[AGNuke]

Never heard of it. I doubt about this knowledge shared in 12th standard, even more so considering the standard of education I've been provided here. I would be grateful if you were to enlighten me briefly on how this hypothesis is established.

Still, as a last resort, I tried using my old habit of giving bluff explanation to support the answer (even if it isn't ) and drew out the structures possible in Hyperconjugation

For I

For II

Since I has 6 structure while II has 5 structures, I is more stable (I know I am talented )

 

[chemisttree]

Brown's hypothesis simply states that exocyclic double bonds to six-member rings are more reactive than double bonds inside the ring and double bonds exocyclic to a five-member ring are more stable than those within the five-member ring. This is supported by reactivity data.