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Topic: Worst proton NMR I've ever seen  (Read 5899 times)

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Offline CopperSmurf

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Worst proton NMR I've ever seen
« on: March 08, 2009, 01:14:59 PM »
I'm stuck on trying to solve this proton NMR problem. Usually they aren't a problem for me unless it involves a lot of J coupling stuff. I'm told that this compound is water insoluble and is a clear colourless liquid that was dissolved in CDCl3 to analyze it in the proton NMR.

The bad part is that there are two broad blobs (peaks) at ~3.8 and ~1.4 ppm. I'm pretty sure that peak at ~3.8 is -OH of an alcohol. The peak at 0.88 ppm is a triplet and the peak at 1.19 is a doublet. The stuff in between 2 and 2.5 ppm I feel are not important and are probably there to mess me up (super low integration). Whoever ran this probably had some leftovers in there. I got a "zoomed in" version posted too.

Then I tried to come up with the best integration ratios (left to right): 1:4:7:3:3 or 1:4:8:3:3. I know for sure there isn't any aromatic rings or phenol in there since there are no chemical shifts above 4 ppm. Now I'm stuck on putting it all together. I also uploaded a .gif file with the original integrations I was given on the bottom and labelled chemical shifts on the top in the proton NMR. I got snacks to give if anyone's willing to help. :)

Offline James Newby

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Re: Worst proton NMR I've ever seen
« Reply #1 on: March 08, 2009, 01:17:33 PM »
Stupid question but do you have any information on what the compound may be?  Mass specs, composition, starting materials etc
4th year undergraduate at the University of Sheffield

Offline CopperSmurf

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Re: Worst proton NMR I've ever seen
« Reply #2 on: March 08, 2009, 01:24:48 PM »
sadly, I have no mass spec or composition given to me and this was not a synthesis problem, otherwise I wouldn't be struggling for so long. All I have is this horribly messy proton NMR and some bits of info given to me: water insoluble alcohol, clear colourless liquid, dissolved in CDCl3 and soluble in diethyl ether, and it was implied in this problem that there's no sulphur, no nitrogen, no halogens. It's complete focus on this proton NMR.

*edit* We've been working on neutral compounds and this would be classified as one of them. I don't know if that helps any to solve this, but I guess getting as much info as possible could lead into something.
« Last Edit: March 08, 2009, 01:46:26 PM by CopperSmurf »

Offline James Newby

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Re: Worst proton NMR I've ever seen
« Reply #3 on: March 08, 2009, 01:55:47 PM »
From the integrations i think:

3-4 protons at 0.9
6 protons at 1.12
3 protons at 1.14
1 proton at 1.4

3-4 protons at 0.9 ia likely to be a terminal methyl group
6 protons at 1.12 are probably CH2 units
3 protons at 1.14 may be methyl group near the OH
1 proton at 1.4 i think is attached to the carbon with the OH on it

so thats 14 protons in your molecule, and 5 environments, very tricky!
4th year undergraduate at the University of Sheffield

Offline CopperSmurf

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Re: Worst proton NMR I've ever seen
« Reply #4 on: March 08, 2009, 03:04:59 PM »
Hm... sounds possible. Maybe an alkene with one alcohol group?

I was thinking along the lines of octanol or heptanol, depending on how many hydrogens there actually is...

Offline James Newby

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Re: Worst proton NMR I've ever seen
« Reply #5 on: March 08, 2009, 03:18:25 PM »
i was thinking hexanol, such as hexan-2-ol. There are many other possiblilities such as cyclopentanol with a methyl group attached.  I dont think its an alkene as the signals appear slightly further up the spectra
4th year undergraduate at the University of Sheffield

Offline CopperSmurf

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Re: Worst proton NMR I've ever seen
« Reply #6 on: March 08, 2009, 03:44:33 PM »
hm, hexanol could work too. Anyways, thank you James for helping me out with this. At least I narrowed it down a bit more.

P.S. I looked up a spectra database for 2-hexanol, 2-heptanol, 2-octanol, 2-nonanol, cyclopentanol and they all look really dead similar to each other, and to this.

Offline alphahydroxy

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Re: Worst proton NMR I've ever seen
« Reply #7 on: March 09, 2009, 07:19:08 AM »
Yeah, I think it must be 2-octanol, for the numbers to work.

alcohol proton = 1H  (although you should never rely on hydroxyl protons even appearing in a spectrum, much less base any integration measurements on them...)

methyl next to hydroxyl = d, 3H

other methyl = t, 3H

remaining protons = gak left over between 1-2 - 1.5 ppm, 11H







Offline frenchy

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Re: Worst proton NMR I've ever seen
« Reply #8 on: March 09, 2009, 10:40:06 AM »
your group at 0.90ppm and the other one at 1.25ppm make me think of pentane or hexane.
PhD student in synthetic Inorganic and Supramolecular chemistry.

Offline CopperSmurf

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Re: Worst proton NMR I've ever seen
« Reply #9 on: March 10, 2009, 03:27:59 AM »
thank you all so much for your input. I finally decided upon 2-octanol as my answer for now.  ;D again, thanks sooooo much!

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