foreverstriving
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Hi Guys, how many different chemical environments are there in propan-2-ol? I believe there's 2- the CH3 groups and the COOH group but the answers say 3 and I can't seem to work out where the 3rd group is or what it even is lool.

Any help would be much appreciated.

Thanks in advance.
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Spudgunhimself
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Are you sure it's not the proton NMR, that would definitely have 3. But yeah, it looks like propan-2-ol would only have 2.
Also, propan-2-ol does not contain a COOH group, which I'm sure you know :P
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username913907
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(Original post by foreverstriving)
Hi Guys, how many different chemical environments are there in propan-2-ol? I believe there's 2- the CH3 groups and the COOH group but the answers say 3 and I can't seem to work out where the 3rd group is or what it even is lool.

Any help would be much appreciated.

Thanks in advance.
propanol doesn't have a COOH, it's an alcohol
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SaFa1237
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A COOH functional group is for carboxylic acids. A carbon NMR of propan-2-ol has two environments, however there are three hydrogen environments.
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foreverstriving
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(Original post by JMaydom)
propanol doesn't have a COOH, it's an alcohol
Apologies for the mistake, I meant to say -CHOH-
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foreverstriving
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(Original post by SaFa1237)
A COOH functional group is for carboxylic acids. A carbon NMR of propan-2-ol has two environments, however there are three hydrogen environments.
Apologies for the mistake, I meant to say -CHOH-, so for carbon NMR it would have two peaks right?
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Borek
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Carbon NMR - 2, proton NMR - 3.
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SaFa1237
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(Original post by foreverstriving)
Apologies for the mistake, I meant to say -CHOH-, so for carbon NMR it would have two peaks right?
Yep, that's right.
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username913907
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Right, assuming this is an NMR question the answer is wrong. The OH proton is totally irrelevant as it will exchange with the D in the solvent and no peak will be observed.
So from a 'actual molecule' point of view there are 3 different proton environments (methyl, CH(Me)2OH and OH) but from an NMR point of view only 2.
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foreverstriving
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Thanks for all the help guys

Posted from TSR Mobile
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Nirgilis
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(Original post by JMaydom)
Right, assuming this is an NMR question the answer is wrong. The OH proton is totally irrelevant as it will exchange with the D in the solvent and no peak will be observed.
So from a 'actual molecule' point of view there are 3 different proton environments (methyl, CH(Me)2OH and OH) but from an NMR point of view only 2.
Why wouldn't the OH peak show up? :curious: . Surely not every OH will have exchanged with solvent for the entire duration of the NMR sample being taken, so a singlet would show up..?

A quick database search shows there to be 3 peaks present :yep:

EDIT: This is for proton NMR :yep:
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foreverstriving
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Thanks for all the help guys- my teacher verified what you all suggested- it would be two peaks for C NMR and 3 for proton NMR.
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username913907
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(Original post by Nirgilis)
Why wouldn't the OH peak show up? :curious: . Surely not every OH will have exchanged with solvent for the entire duration of the NMR sample being taken, so a singlet would show up..?

A quick database search shows there to be 3 peaks present :yep:

EDIT: This is for proton NMR :yep:
Think about 2 things..... 1. NMR is very insensitive. You really don't get an idea for just how insensitive it is compared to e.g. mass spec
2. There are far more D's coming from the solvent than H's you put in from the sample. If they can equilibrate with each other then there will be a minute signal from the exchangeable protons.
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Borek
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H-D exchange takes place from the moment you mix the samples. No idea how fast the reaction is, but here they state

This exchange, which is catalyzed by acid or base, is very fast under normal conditions, since it is difficult to avoid traces of such catalysts in most experimental systems
so I suppose in typical situation H-D exchange can reach the equilibrium before the spectrum is recorded.
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BJack
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(Original post by JMaydom)
Think about 2 things..... 1. NMR is very insensitive. You really don't get an idea for just how insensitive it is compared to e.g. mass spec
2. There are far more D's coming from the solvent than H's you put in from the sample. If they can equilibrate with each other then there will be a minute signal from the exchangeable protons.
That's all very well, but I have a 2-propanol spectrum in front of me and there's a clear peak from the alcoholic proton at 2.16ppm.
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username913907
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(Original post by BJack)
That's all very well, but I have a 2-propanol spectrum in front of me and there's a clear peak from the alcoholic proton at 2.16ppm.
whats the solvent?
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BJack
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(Original post by JMaydom)
whats the solvent?
CDCl3
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Borek
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-OH protons in D2O are replaced by D and they don't give a signal, in CDCl3 they are not replaced, and they give a signal.

At least that's my understanding, last time I did any NMR was while Thatcher was a Prime Minister.
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username913907
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(Original post by Borek)
-OH protons in D2O are replaced by D and they don't give a signal, in CDCl3 they are not replaced, and they give a signal.

At least that's my understanding, last time I did any NMR was while Thatcher was a Prime Minister.
YOU OLD..... :P
(Original post by BJack)
CDCl3
mmm, i thought they'd exchange.... obviously not acidic enough.
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