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Author Topic: Need help identifying a compound  (Read 2286 times)

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Orgodude

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Need help identifying a compound
« on: December 09, 2012, 12:46:22 PM »

Hey guys,

So I'm supposed to figure out an unknown compound based on these 4 readings from a Mass spectrometry, a C13 NMR, a Proton NMR and an IR Spectra. While I have a basic understanding of how to read these graphs, there seems to be so many caveats i'm pretty stuck.

Here they are pictured below, if you guys know how to approach this, any help would be greatly appreciated.




Links if its easier to view:
http://imgur.com/2eQcj
http://imgur.com/laFGY
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jdpaul88

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Re: Need help identifying a compound
« Reply #1 on: December 09, 2012, 02:52:05 PM »

that is cyclohexanol. you have an OH at 70.11 ppm
The spectrum for carbon shifts can be found here
http://chemistry.umeche.maine.edu/CHY251/NMR-Table.html
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jdpaul88

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Re: Need help identifying a compound
« Reply #2 on: December 09, 2012, 02:52:58 PM »

you can use http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi to verify that it is cyclohexanol. It contains H NMR, C NMR, IR, Ramen, and Mass Spec
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Orgodude

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Re: Need help identifying a compound
« Reply #3 on: December 09, 2012, 03:14:33 PM »

Wow this website is amazing man. Thanks so much.
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MOTOBALL

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Re: Need help identifying a compound
« Reply #4 on: December 10, 2012, 01:18:12 PM »

While I don't want to spoil the party..

1. this site is not meant to give you pat answers to course problems.

2. you should show us your attempts and where you get stuck, so that we can guide you

3. when you get a similar question on a finals paper (not take-home) as you will you need to know interpretation of this type of data

4. I don't know if the unknown is cyclohexanol or not, but if it is the mass spectrum is NOT labelled correctly; the peak at m/z 82 is not the "parent peak".  That nomenclature is only used with respect to MS/MS spectra; if you mean "molecular ion( M+[sup].[/sup]), then that would be the peak at m/z 100, if this cyclohexanol.

5. you should approach this by interpreting each spectrum to find functional groups (e.g. -CO; -NH2; >C=C<; -OH etc); numbers of equivalent C or H atoms etc.  Then combine information to suggest possible structure(s)
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Orgodude

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Re: Need help identifying a compound
« Reply #5 on: December 10, 2012, 06:42:19 PM »

my intention wasn't just for a quick answer or anything, it was just cool to have a site in which i could double check my solutions. It actually isn't cyclohexanol i dont think.

From the MS i can tell there is an OH group present, but i was wondering what the indentation at 2700 indicates? or is that not significant? The dent just below the 3000 means its aliphatic correct?

Also i realize i mislabeled the MS readout
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Orgodude

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Re: Need help identifying a compound
« Reply #6 on: December 10, 2012, 06:49:31 PM »

also the Proton NMR has too many peaks for something like cyclohexane
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Orgodude

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Re: Need help identifying a compound
« Reply #7 on: December 10, 2012, 07:01:52 PM »

Where i'm getting stuck is that if this compound has a mass of 100g, then accounting for an OH group that brings it to 83.

If there were 6 carbons that would mean there are 12 Hydrogens, but there's no arrangement of C6H12O that i can make work with the proton NMR that was provided
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discodermolide

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Re: Need help identifying a compound
« Reply #8 on: December 10, 2012, 07:02:53 PM »

Is this statement actually true?
How many protons does cyclohexanol have?
How many peaks may you expect?
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jdpaul88

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Re: Need help identifying a compound
« Reply #9 on: December 10, 2012, 07:17:05 PM »

I would use the resources I gave you. Also, be sure to memorize a HNMR shift spectrum. It will help tremendously
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Orgodude

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Re: Need help identifying a compound
« Reply #10 on: December 10, 2012, 07:45:36 PM »

Is this statement actually true?
How many protons does cyclohexanol have?
How many peaks may you expect?


Ah, you're right. Cyclohexanol has 12 hydrogens. After drawing it and comparing the Hydrogens, it does look like it should have 7 peaks. For some reason i was thinking that cyclohexanol possessed several equivalent hydrogens when in fact it appears that none of them are. I'm going to study the splitting to be sure.

I would use the resources I gave you. Also, be sure to memorize a HNMR shift spectrum. It will help tremendously

The site actually has been very helpful. I've been looking at lots of different compounds. I am also working on memorizing the shift spectrum(s).
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Orgodude

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Re: Need help identifying a compound
« Reply #11 on: December 10, 2012, 07:48:59 PM »

I think however the IR spectrum for Cyclohexanol on that website is incorrect?



It doesn't have the dip in the 3500-3200 range that would be expected from an alcohol. Unless there is some other factor i'm failing to consider.

-Also, looking at the MS spectra, I assume the peak at the 82 mark is the Cyclohexane broken away from the hydroxy group. But what would account for the base peak @ 57?
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discodermolide

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Re: Need help identifying a compound
« Reply #12 on: December 10, 2012, 08:05:57 PM »

This is a solution IR you show. The peak intensity is dependant upon the concentration of the sample.
What was your original IR recorded in, neat, solution, what?
Think about cyclohexanol it's NMR spectrum, which hydrogens are equivalent and which not? Make a model, are all the protons equivalent? (apart from the OH and CH protons of course)
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Orgodude

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Re: Need help identifying a compound
« Reply #13 on: December 10, 2012, 08:14:10 PM »

Where would i look to determine what the IR sample was recorded in?

As for the NMR, wouldn't all of the Hydrogen's in it not be equivalent?
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jdpaul88

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Re: Need help identifying a compound
« Reply #14 on: December 10, 2012, 08:19:19 PM »

think about labeling the protons on a phenyl ring. Some will be equivalent but some wont. And you know the hydroxy group will also contribute a single line to the HNMR
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