Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: eureka123 on November 01, 2009, 10:10:40 PM
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I have no clue about this question....
Plz discuss this one...
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As this mechanism in my figure
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Check your atom count.
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Sorry,the correct figure has been upload
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If you have in intramolecular reaction of 15 carbons, shouldn't the product also contain 15 carbons?
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Sorry but options are
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I also found this...can anyone explain this all ?
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Eureka, are you sure you drew those structures right? I am pretty certain that the product is not one of the two that you drew (close, but not exactly what you drew).
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Yes sir,
These are the 2 options..
but the book may be wrong also..
btw plz explain that abstract from a book which I gave in my last post
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Well, my issue with those two answers is that the first would require an overall oxidation of the substrate, and the second would require the loss of a carbon. First off, PPA is not really an oxidant. Second, the loss of a carbon is possible, but I would say unlikely under these conditions with this substrate.
The excerpt from the book is kind of an overview of PPA's common uses, but I don't think it is super useful in the context of this question.
What is the context of this question in the book? What chapter is it from?
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Sir ,that abstract is from a book named "Challenges in synthetic organic chemistry"
in chapter "Dehydration reactions "
So whats the final answer anyway ??
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The following seems a logical path.
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Any comments on what our friend "orgopete" has done ?
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I think organopete has the right product, but the mechanism is missing a little subtlety. I don't want to give it away though – any guesses?
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Not really. I'm curious though. Does it have to do with the placement of the carbocations?
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Not really. I'm curious though. Does it have to do with the placement of the carbocations?
Sort of, but really as a consequence of something else that would cause some of the carbocations to be in other places.
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As in a hydride shift? We've only began talking about this stuff... :-\
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movies? I really do want to know what's missing...
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I believe that this is a Nazarov cyclization (http://en.wikipedia.org/wiki/Nazarov_cyclization_reaction) and therefore would be a pericyclic reaction with all four electrons moving at once.
The wiki mechanism is very lacking. I have most commonly seen it drawn like this:
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Thanks, movies. :)
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wat is PPA doing here???
is it used only to activate the carbonyl ??
if so can't we use any other acid ??
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In principle, yes you could use another acid. PPA is quite a strong acid and tends to be very effective for a lot of Brønsted acid-catalyzed transformations. It has some advantages as well since it is very cheap, relatively easy to handle, is able to absorb trace amounts of water without ill effects, and can be removed in workup easily because it is soluble in large amounts of water.
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PPA also provides a highly polar environment which can have a dramatic effect on reactivity. It can be a challenge to work with though, it is very viscous and the workup often involes lots and lots of hot water (to hydrolyse and dissolve the various phospho species), but it is highly effective, especially in Friedel-Crafts and Nazarov type reactions.
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So whose mechnaism is better ??
orgopete's or movies' ??
or are both exactly same ??
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Movies is better in that it is a mechanism. I was reading from the original posts that there was some reasonable expectation of what was going to happen, but errantly included an incorrect number of atoms. For me, that has always been a source of frustration as this seemed to be the simplest level of checking whether an answer is reasonable or not. When I posted, I did not offer up a mechanism per se. It was just a listing of probably intermediates that might lead to a likely product. Movies foresaw this problem as having more mechanistic value and noted this, hence even posting a mechanism.
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kk..
thanx