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Topic: Help with a mechanism  (Read 3694 times)

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Offline Aldehyde

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Help with a mechanism
« on: October 26, 2012, 11:48:32 PM »


How do I start this problem? I know that the OH- should take out a beta hydrogen from either sides, but I am unsure how do they get the form. I know that single bonds can freely rotate, but I still can't see it. Any advice? I doubt is it possible to do an ethy shift since it would be unpractical.
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Offline discodermolide

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Re: Help with a mechanism
« Reply #1 on: October 27, 2012, 01:19:17 AM »
Think about SN2 reactions.
« Last Edit: October 27, 2012, 01:52:09 AM by discodermolide »
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Offline Aldehyde

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Re: Help with a mechanism
« Reply #2 on: October 27, 2012, 01:28:29 AM »
Thank you I got it.  :)

Can you explain why is it an Sn2 reaction and not a E2 reaction? I thought that for something like OH- that E2 reaction would be more dominate for a secondary carbon. Is there an exception that I am missing?
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Offline discodermolide

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Re: Help with a mechanism
« Reply #3 on: October 27, 2012, 01:33:55 AM »
Quote from: Aldehyde on October 27, 2012, 01:28:29 AM
Thank you I got it.  :)

Can you explain why is it an Sn2 reaction and not a E2 reaction? I thought that for something like OH- that E2 reaction would be more dominate for a secondary carbon. Is there an exception that I am missing?

Wait did you draw the structure incorrectly? You suddenly have a primary alcohol not a secondary one which would be the product.
I did not notice that.
Sorry
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Offline Aldehyde

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Re: Help with a mechanism
« Reply #4 on: October 27, 2012, 01:40:31 AM »
No I did not draw it wrong, everything is correct. A same thread talking about the same problem: http://forums.studentdoctor.net/showthread.php?t=924882

???
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Offline discodermolide

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Re: Help with a mechanism
« Reply #5 on: October 27, 2012, 01:51:48 AM »
Then I'm sorry I misread the structure. Ignore what I posted. I will get back to you.
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Offline discodermolide

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Re: Help with a mechanism
« Reply #6 on: October 27, 2012, 02:04:08 AM »
OK here is what I think is going on.
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Offline Aldehyde

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Re: Help with a mechanism
« Reply #7 on: October 27, 2012, 02:08:49 AM »
Wow, I would never in my entire life thing of something like that.  :o

I have a lot of learning to do, it is a shame that the text book doesn't even mention these kind of things, do you happen to have a name of this type of mechanism?

Thank you again.
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Offline discodermolide

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Re: Help with a mechanism
« Reply #8 on: October 27, 2012, 02:29:23 AM »
Well it is 1 internal SN2 reaction followed by a ring opening. I don't think it has a name.
« Last Edit: October 27, 2012, 02:44:49 AM by discodermolide »
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Offline Dan

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Re: Help with a mechanism
« Reply #9 on: October 27, 2012, 03:44:13 AM »
Quote from: Aldehyde on October 27, 2012, 02:08:49 AM
Wow, I would never in my entire life thing of something like that.  :o

I have a lot of learning to do, it is a shame that the text book doesn't even mention these kind of things, do you happen to have a name of this type of mechanism?

It is an example of neighbouring group participation (NGP). That may be a useful search term if you wan't to do more reading.

e.g. http://en.wikipedia.org/wiki/Neighbouring_group_participation

NGP is a very broad term that covers many different types of mechanism. In your case the NGP is an SN2 reaction (as has been said).
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