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TBR Organic 1, Ch. 3, Passage II, Q4

Pose

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I'm sorry I can't upload the image from the book, so hopefully someone has a copy nearby.

The question asks:

Which carbons in (-)-carvone can carry a positive charge, if carvone is treated with strong acid?

This seems like an easy thing to do, but I don't really understand the explanation. It's been a while since I have taken organic chemistry.

Thanks!
 
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Gauss44

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I'm sorry I can't upload the image from the book, so hopefully someone has a copy nearby.

The question asks:

Which carbons in (-)-carvone can carry a positive charge, if carvone is treated with strong acid?

This seems like an easy thing to do, but I don't really understand the explanation. It's been a while since I have taken organic chemistry.

Thanks!

carvone + H2SO4 = carvacrol

"Treatment of carvone with strong acid promotes reaction of the non-conjugated alkene to react with the acid to generate a carbocation..." Source is the paragraph above figure 2 here:
http://www.organicchem.org/oc1web/exp/carvone/carvonedes.html
 
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enervate

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There are two things going on here:

1) The electrons involved in the carbonyl resonate out to the oxygen. This makes oxygen negatively charged so it will quickly pick up a proton but that leaves C_a positively charged. Since the double bond between C_c and C_b is immediately adjacent, it can resonate to C_a to neutralize the positive charge on but that leaves C_c with a positive charge. Since there aren't any negatively charged species such as Period VII elements involved in this reaction, neither positive charge will ever be truly satisfied. That double bond will just resonate between C_c - C_b and C_b - C_a and leave positive charges on both C_c and C_a.

2) That double bond between C_e and C_f is going to take a proton, but which one? Since C_e is tertiary, it won't be terribly upset having a positive charge. C_f is primary so it would not be pleased to have a positive charge. Instead, it's going to take on that proton and leave C_e with a positive charge.

Be sure to draw out your resonance structures!
 
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