Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Orgodude on December 09, 2012, 06:46:22 PM
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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.
(http://i.imgur.com/2eQcj.jpg)
(http://i.imgur.com/laFGY.jpg)
Links if its easier to view:
http://imgur.com/2eQcj
http://imgur.com/laFGY
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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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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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Wow this website is amazing man. Thanks so much.
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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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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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also the Proton NMR has too many peaks for something like cyclohexane
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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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Is this statement actually true?
How many protons does cyclohexanol have?
How many peaks may you expect?
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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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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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I think however the IR spectrum for Cyclohexanol on that website is incorrect?
(http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?imgdir=ir&fname=NIDA8688&sdbsno=581)
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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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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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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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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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?
What about axial and equatorial protons are they equivalent?
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I wasn't aware that i should be looking at the hydrogen's in the context of whether or not they are in the axial or equatorial position. I'm not exactly sure how to approach that..
I would guess that they are not. 2 axial protons wouldn't be equivalent when an electronegative atom is effecting the symmetry of a compound. does my thinking make sense?
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Well the axial and equatorial protons are not magnetically equivalent. When the spectrum is recorded at RT you see time averaged signals for both sets of protons, i.e. one big lump of protons. This is due to the ring flip mechanism. If you cool the sample down to say liquid nitrogen temperatures you see two distinct sets of signals, each of 6 protons each, one for the axial one for the equatorial protons. If you do this experiment properly you can actually measure the rate of the ring flipping process.
Your NMR does not look like the one shown on that web site provided by the other poster.
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It appears that you have two different compounds. The carbon NMR matches exactly the one you have listed
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Ahh every time i feel like i'm beginning to grasp the material a new variable is introduced.
Is it possible that the reason the NMR from the website doesn't resemble the NMR from my homework is due to such a scenario as you've described? The problem is entirely hypothetical, and the readings are not from any actual product that I have produced.
When I'm looking at a cyclohexanol drawing, to me it looks like the environment's of the hydrogens differ from carbon to carbon, but i'm not sure (certainty seems like a luxury in Organic.) I'm able to identify 7 distinct groups,a hypothesis which is supported by my NMR. This is partly why the data from the website is so confusing to me.
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Your NMR also accounts for 12 Hydrogens, right
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It appears that you have two different compounds. The carbon NMR matches exactly the one you have listed
I was wondering if this was the case. We were only supposed to have one compound though, so maybe it was a mistake?
The range of peaks on my NMR (to the right of the OH peak) fall within the same range as those spikes in the NMR from the site. I dont know if that's significant.
Also, the IR from the website doesn't have the alcohol bend around the 3500-3200 range. I know disco mentioned the conditions of the sample can affect this, but i think it'd be strange that the site would would throw that kind of curve ball. Maybe there's a mistake on the sites part?
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The aromatic portion would show a higher proton shift than what it is - something such as 7.5 ppm...this makes me wonder if the carbon is referring to cyclohexanol and the h nmr is referring to something different
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Your NMR also accounts for 12 Hydrogens, right
I'm not so good with the splitting and whatnot, so i'm not sure.
It does fit in when u consider the H on the OH, the one on the C-OH, and then each of the pairs on the remaining 5 carbons. That adds up to 7 environments, 12 H's total.
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The OH is present in the IR. As I said the intensity is dependant upon concentration. You can used these dilution effects to establish H-bonding in a compound.
Maybe the 1H-NMR was run at low temperature?
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The aromatic portion would show a higher proton shift than what it is - something such as 7.5 ppm.
Is it aromatic though? I thought aromatic indicates double bonds.
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Nevermind that is the shift of a carboxylic acid
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The aromatic portion would show a higher proton shift than what it is - something such as 7.5 ppm.
Is it aromatic though? I thought aromatic indicates double bonds.
Oh yes, I was thinking of aromatic, sorry. You're right
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The OH is present in the IR. As I said the intensity is dependant upon concentration. You can used these dilution effects to establish H-bonding in a compound.
Maybe the 1H-NMR was run at low temperature?
Do you mean the IR from the website or the one i provided?
I'm only familiar with alcohols showing like this on IR spectra:
http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ch13/figures/iriproh.gif
Doesn't it seem strange that the site would have an IR for an alcohol, but under unique conditions in which the most recognizable signifiers are not there?
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Ohhh i just saw, the IR from the site i posted was in CCl4 solution; the IR in "liquid film" matches the one from my example.
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?imgdir=ir&fname=NIDA8688&sdbsno=581
vs
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?imgdir=ir&fname=NIDA9018&sdbsno=581
HNMR
90 mhz
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?fname=HSP00009&imgdir=hspW
vs
400 mhz
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/IMG.cgi?fname=HSP40238&imgdir=hspW
So it is indeed cyclohexanol.
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The IR on that web site was run in solution, it shows the OH as a sharp signal around 3700 cm-1 as well as everything else. It is correct.
Your IR was run under different conditions, possibly as a neat sample, accounting for the very large broad OH signal.
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Lol, now i'm going to get some sleep. Thanks for sweating this out with me Paul, Disco. I appreciate it.