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Author Topic: Could someone please help me figure out this spectrum?  (Read 2195 times)

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kaeyre

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Could someone please help me figure out this spectrum?
« on: April 27, 2017, 03:21:20 PM »

I'm trying to figure out this spectrum for my unknown, but I've only ever been used to interpreting NMR given in problems, not a real NMR sheet, so I'm struggling quite a bit. All I know about the molecule is that it is an alcohol, and it is likely a 3 degree (but that doesnt seem possible from this spectrum) or 2 degree alcohol.
My problem is that no molecule I come up with has the appropriate number of hydrogens.. I don't know if i'm messing up because the integration is in decimals and i'm not used to it being that way or because I can't count the peaks here... but if someone could please help me I would very much appreciate it. My best try at it is something like 3-pentanol but I doubt it's correct..
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wildfyr

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Re: Could someone please help me figure out this spectrum?
« Reply #1 on: April 28, 2017, 04:46:48 AM »

This is a classical spectrum of a linear long chain alcohol. If you double the assigned integration values it will become clear. The peaks and their shape at 1.3 ppm and 0.9 ppm are the giveaway. There are 8 CH2 groups with very similar electronic environments along the bulk of the chain, then the terminal CH3 is the most electron rich at 0.9 ppm. The the CH2 group beta to the hydroxy is at 1.7, then the one alpha to the hydroxy gets the widest separation at 3.7 since its being directly affected by the alcohol. I would judge this 1-undecanol.

Look at the HNMR spectrum of the very similar 1-decanol on SDBS and youll see the similarity

 http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
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kaeyre

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Re: Could someone please help me figure out this spectrum?
« Reply #2 on: April 28, 2017, 09:14:52 AM »

This is a classical spectrum of a linear long chain alcohol. If you double the assigned integration values it will become clear. The peaks and their shape at 1.3 ppm and 0.9 ppm are the giveaway. There are 8 CH2 groups with very similar electronic environments along the bulk of the chain, then the terminal CH3 is the most electron rich at 0.9 ppm. The the CH2 group beta to the hydroxy is at 1.7, then the one alpha to the hydroxy gets the widest separation at 3.7 since its being directly affected by the alcohol. I would judge this 1-undecanol.

Look at the HNMR spectrum of the very similar 1-decanol on SDBS and youll see the similarity

 http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi
Thank you, this has really helped to clear this up a bit
i've checked my table of unknowns and it appears that 1-undecanol isn't a possibility for this molecule. 1-decanol is a possibility, but then the issue with the hydrogen count returns.. is it at all possible that this spectrum could be of a secondary alcohol? or could it only be primary?
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wildfyr

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Re: Could someone please help me figure out this spectrum?
« Reply #3 on: April 29, 2017, 04:32:04 AM »

I think they flubbed the answer key. That is undecanol. 2 2 16 3. I've seen enough linear alkanes with a functional group at the end to recognize one when it see it. You get a similar spectrum for almost any molecule like this. Go to your professor and show them this spectrum with 1-undecanol drawn on it and the peaks assigned.
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