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Decreasing Order of Stability in unsaturated 6C Rings

  1. Nov 17, 2012 #1

    AGNuke

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    Decreasing Stability order of given I, II, III, IV (in order)
    cho2.png

    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?
     
  2. jcsd
  3. Nov 18, 2012 #2

    chemisttree

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    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?
     
  4. Nov 18, 2012 #3

    AGNuke

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    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 :tongue:) and drew out the structures possible in Hyperconjugation

    For I
    HC1.png

    For II
    HC2.png

    Since I has 6 structure while II has 5 structures, I is more stable :biggrin: (I know I am talented :blushing:)
     
  5. Nov 19, 2012 #4

    chemisttree

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    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.
     
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