Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: mjoa123 on December 05, 2012, 09:09:36 PM
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In lab we had to do tests in order to find out what our compounds are, but I have no idea where to even start. Is anyone good with this stuff?
My compound only contains H, C, and O. It is a clear liquid (basically looks like water). The boiling point is around 94° C. The refractive index is 1.38 nD. It is not soluble in water, HCl, or NaOH. It is soluble in chloroform.
I also ran NMR test and an IR spectrum. It is hard to describe the IR spectrum, but if needed I will.
The NMR had these peaks:
-Three peaks at: 4.0408, 4.0239, 4.0070
-One peak at: 2.0521
-Six peaks at (this is odd, but I asked and it can be correct, which might be a giveaway as to what my compound is?): 1.6965, 1.6778, 1.6605, 1.6422, 1.6249, 1.6067
-Three peaks at: 0.9627, 0.9441, 0.9255
Any help here? I am actually really quiet terrible in chemistry, unfortunately. Thanks.
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If the three peaks at 0.9 ppm were a methyl group, then how many hydrogens are present on the carbon this memthyl group is attached? It is also very useful to give the integral for the peaks. You can virtually determine the molecular formula from the NMR & IR.
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If the three peaks at 0.9 ppm were a methyl group, then how many hydrogens are present on the carbon this memthyl group is attached? It is also very useful to give the integral for the peaks. You can virtually determine the molecular formula from the NMR & IR.
Thanks for the help. I managed to take pictures of both the NMR and the IR spectrum. They are not the best pictures but hopefully they are legible.
NMR:
http://www.imagebam.com/image/c55f08224404309 (http://www.imagebam.com/image/c55f08224404309)
IR spectrum:
http://www.imagebam.com/image/90a1b4224404313 (http://www.imagebam.com/image/90a1b4224404313)
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There's an additional options button on a posting page that allows you to attach images to this forum. I would've done it for you, but the images don't appear in the Imagebam page.
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There's an additional options button on a posting page that allows you to attach images to this forum. I would've done it for you, but the images don't appear in the Imagebam page.
You can't see the images when clicking on the links?
I did put the images with the "[ img ] [ / img ] (without the spaces)" but they didn't show up.
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The coupling pattern in the NMR should help you find out what this compound is.
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The coupling pattern in the NMR should help you find out what this compound is.
I posted the NMR in post #3, can you see it?
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I saw both spectra by clicking on the links you gave.
What do you know about coupling patterns in the NMR spectrum?
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I saw both spectra by clicking on the links you gave.
What do you know about coupling patterns in the NMR spectrum?
Pretty much nothing. I know that they took out water and chloroform from the graph. I think that the ppm tells the amount of each element but that it's not always accurate I believe. I looked for a guide that would match the numbers with an element so that I can maybe connect the puzzle but couldn't find anything. Have no clue :-\
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ppm in this case refers to the chemical shift references to TMS (tetramethylsilane) which is 0.
Have a look here
http://en.wikipedia.org/wiki/Proton_NMR (http://en.wikipedia.org/wiki/Proton_NMR)
I can't teach you about H-NMR here, so you will have to start perhaps with that web page.
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ppm in this case refers to the chemical shift references to TMS (tetramethylsilane) which is 0.
Have a look here
http://en.wikipedia.org/wiki/Proton_NMR (http://en.wikipedia.org/wiki/Proton_NMR)
I can't teach you about H-NMR here, so you will have to start perhaps with that web page.
How do I know if the lines are an H, C, or an O?
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The signals in the spectrum correspond to the hydrogens in the molecule. The position gives you information at to its chemical environment. The number of lines tells you how many hydrogens are on the adjacent carbons.
So for example a CH3 group attached to an oxygen atom would appear at a different place to a CH3 group attached to another carbon atom.
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The signals in the spectrum correspond to the hydrogens in the molecule. The position gives you information at to its chemical environment. The number of lines tells you how many hydrogens are on the adjacent carbons.
So for example a CH3 group attached to an oxygen atom would appear at a different place to a CH3 group attached to another carbon atom.
So the first 3 lines means there are 3 hydrogen atoms attached to either an oxygen or carbon? The the huge line means one hydrogen attached in the middle, then what about the 6 lines?
And is there a way to know if it's attached to an oxygen or carbon atom?
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The numbers under the lines in the spectrum tell you how many hydrogens are sitting on the carbon, although in your example they look a little off to me.
In the link I provided there is a table of chemical shifts. Use that to decide if it is attached to an oxygen atom or something else.
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The numbers under the lines in the spectrum tell you how many hydrogens are sitting on the carbon, although in your example they look a little off to me.
In the link I provided there is a table of chemical shifts. Use that to decide if it is attached to an oxygen atom or something else.
So there are 4 Hydrogens attached to the carbon, or 2.70 (aka 3)? And what does the number of lines mean then?
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As I said I think the integration is not quite correct. at 2.70 there are 2 hydrogens attached.
The lines tell you how many hydrogen atoms are on the adjacent carbon atom, formula n+1, where n is the number of hydrogens. The intensity of the lines follows Pascal's triangle, 1, 1,1 1, 2, 1, 1,3,3,1 and so on. So for example if you saw 4 lines with intensities of 1,3,3,1 (a quartet) it's neighbouring C atom has 3 hydrogens attached to it. That is n+1 where n is the number of neighbouring hydrogens.
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As I said I think the integration is not quite correct. at 2.70 there are 2 hydrogens attached.
The lines tell you how many hydrogen atoms are on the adjacent carbon atom, formula n+1, where n is the number of hydrogens. The intensity of the lines follows Pascal's triangle, 1, 1,1 1, 2, 1, 1,3,3,1 and so on. So for example if you saw 4 lines with intensities of 1,3,3,1 (a quartet) it's neighbouring C atom has 3 hydrogens attached to it. That is n+1 where n is the number of neighbouring hydrogens.
So I now know that the compound starts off with a Carbon atom with 3 Hydrogen atoms attached to it. On the NMR there is a long single line that's a 2.0521 ppm. I can't remember if they told me if that was chloroform or water or if that is an actual part of the compound. So it's just one line, so I assume that there is just one of it. It has to be either C, H or O. I may be totally off here though?
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Is it methyl propanoate (C4O8H2)? I think I have narrowed it down to a few that could possibly be it but I can't find any decisive one.
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No it's not methyl propionate, but good guess faulty reasoning.
So you have a CH3 group in your molecule which displays as a triplet, this means it is next to a carbon atom that has 2 hydrogens on it.
The signal at 2.05 is neither water nor chloroform.
It is a singlet, meaning it has neighbours with atoms not having hydrogen to them, so what could that be?
And the signal with 5 lines? What does that tell you?
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No it's not methyl propionate, but good guess faulty reasoning.
So you have a CH3 group in your molecule which displays as a triplet, this means it is next to a carbon atom that has 2 hydrogens on it.
The signal at 2.05 is neither water nor chloroform.
It is a singlet, meaning it has neighbours with atoms not having hydrogen to them, so what could that be?
And the signal with 5 lines? What does that tell you?
Hmmm.. well doesn't methyl propionate have 2 H atoms on the 2nd carbon?
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What does the IR tell you?
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What does the IR tell you?
I think it tells me where the C-O groups are? If I remember correctly. In the previous post, were you saying the 2nd carbon has 2 H atoms on it or that it does not? Is the first carbon atom with 3 H atoms attached the singlet, meaning the carbon next to it has an Oxygen atom attached?
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Okay, you are close. Let's review. There are two methyl groups, one has a CH2 attached and the other, none. There are two other CH2 groups. Logically, they are connected. I think you had that. I presume you learned from the IR a C=O and C-O bond were present, also consistent. If you look at a table of chemical shifts, an atom attached to a oxygen atom will be shifted much further down than one attached to a carbon. One of the CH2 groups is shifted to about 4 ppm. With your MF, what is he compound?
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No I said that the first carbon is attached to a carbon carrying 2 hydrogens.
The singlet corresponds to a CH3 group but has no neighbours having carbons carrying hydrogen atoms. Which is why I asked about the IR.
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But isn't the CH3, the carbon in CH3 the first carbon atom?
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There are two CH3 groups in this molecule.
Look at Orgopete's summary.
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There are two CH3 groups in this molecule.
Look at Orgopete's summary.
Hmmm.. well I know there is a CH3 at the beginning and in the end, but doesn't that mean the first carbon has 3 Hydrogen atoms attached? So how could the first carbon have 2 hydrogens attached?
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You are not reading carefully. I said that one of the CH3 groups is attached to a carbon carrying two hydrogens, a CH2 group.
So you have CH3-CH2-Unknown-Unknown-Unknown-CH3.
Look at the IR
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Hmmm.. I think it's methyl butanoate? It also matches my boiling point. Is it methyl butanoate or methyl butyrate?
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No it's not them. I can see you reasoning.
Go back to
http://en.wikipedia.org/wiki/Proton_NMR (http://en.wikipedia.org/wiki/Proton_NMR)
and look at the table.
Think about the triplet at 4.1 ppm. What does that mean?
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No it's not them. I can see you reasoning.
Go back to
http://en.wikipedia.org/wiki/Proton_NMR (http://en.wikipedia.org/wiki/Proton_NMR)
and look at the table.
Think about the triplet at 4.1 ppm. What does that mean?
NO2?
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Where did NO2 come from? The table gives the shifts of protons attached to such groups.
PROTONS.
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Where did NO2 come from? The table gives the shifts of protons attached to such groups.
PROTONS.
Eh.. I have no clue if I'm even looking at the same table. At 4.1 on CH3 it says NO2 to the right of it.
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Look at OCOR also says 4.1. also look at COR shifts in the table.
I can't remember the shifts exactly in your NMR, again what does the IR tell you?
remember we have
CH3-CH2-Unknown-Unknown-Unknown-CH3
Just 3 unknown groups/atoms to go
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Look at OCOR also says 4.1. also look at COR shifts in the table.
I can't remember the shifts exactly in your NMR, again what does the IR tell you?
remember we have
CH3-CH2-Unknown-Unknown-Unknown-CH3
Just 3 unknown groups/atoms to go
Is it a methyl or ethyl?
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Is what a methyl or ethyl?
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Is what a methyl or ethyl?
My compound. Sorry I'm really dumb when it comes to this stuff, I can't believe you've stuck around.
I mean does the name start with methyl or ethyl or propyl? I'm thinking it's ethyl ethanoate?
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Neither.
Consider the signal at 2.05, the singlet. Look at the table, what does it correspond to? It looks like COCH3 to me.
So we have CH3-CH2-Unknown-Unknown-C=O-CH3, that is an acetate at one end.
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Neither.
Consider the signal at 2.05, the singlet. Look at the table, what does it correspond to? It looks like COCH3 to me.
So we have CH3-CH2-Unknown-Unknown-C=O-CH3, that is an acetate at one end.
Are you sure the oxygen is attached to both C and CH3?
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Sorry my fault, Look at the picture, THe X represent those groups you have not found yet.
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Well I'm assuming the two that are left are both CH2. Still have no idea what it's called though :/
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No they are not both CH2, only one is. Back to the NMR, the signal at 4.1 is a triplet, meaning it is attached to a carbon bearing 2 hydrogens. The 4.1 signal for this group also means something else according to the table it could be attached to oxygen. What do you think?
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No they are not both CH2, only one is. Back to the NMR, the signal at 4.1 is a triplet, meaning it is attached to a carbon bearing 2 hydrogens. The 4.1 signal for this group also means something else according to the table it could be attached to oxygen. What do you think?
So one of them is CH2 and the other is CO?
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YES, so what we have is propyl acetate.
Attached is a calculated NMR of the compound. Compare it to yours.
One thing, please explain the 5 lines at around 1.75 to me.
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Come on we are nearly there.
Is the other one CO or something else?
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YES, so what we have is propyl acetate.
Attached is a calculated NMR of the compound. Compare it to yours.
One thing, please explain the 5 lines at around 1.75 to me.
There are 6 lines there, right?
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Yes in your spectrum, one of them looks like water (the very left broad peak).
There are actually 5 lines.
It is the middle CH2 with 4 neighbouring hydrogens, n+1 gives 5 lines.
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Yes in your spectrum, one of them looks like water (the very left broad peak).
There are actually 5 lines.
It is the middle CH2 with 4 neighbouring hydrogens, n+1 gives 5 lines.
My professor was wrong then. Further proving his helpfulness. Thanks so much mate, sent you a PM also. Really appreciate your time, you're a very nice person.
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Thank you.
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Hmmm.. I think it's methyl butanoate? It also matches my boiling point. Is it methyl butanoate or methyl butyrate?
While methyl butanoate has a CH3 singlet and two CH2 groups, the lowest peak in the spectrum would be the methyl singlet as it is attached to an oxygen atom. Isn't it a CH2 attached to an oxygen?