NMR question that is annoying the hell out of me

[Thearchitect]

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C9H10O3

There is a doublet(2H) at 7, a doubet(2H) at 8, and a doublet(6H) at 3.9.

Been staring at this forever. Nothing works to give that NMR. I think the question is BS.

 

[Thearchitect]

I changed the H count. Sorry about that.

It's gotta be a para substituted benzene ring. But I can't figure out how to get the single signal doublet, espceially one that is a 6H integration.

 

[Medikit]

I can't really figure out how you get an integration of 6 with 9 carbons and a benzene ring. I don't see how you get a doublet with an integration of 6 without getting a quadruplet or triplet somewhere else, but I never really learned some of the more obscure aspects of splitting.

 

[Thearchitect]

Actually, the integration is 1:1:3. But it turns out to be 2h/2h/6h. You probably knew that though. I don't know myself what is up with that problem. It doesn't work.

 

[Sahani]

Working on it. Sort of fun... sort of sad it's sort of fun.

 

[Thearchitect]

Working on it. Sort of fun... sort of sad it's sort of fun.

No luck huh? There is only a small amount of ways to connect C3H603 to a para sub'd benzene ring, and I think I've exhausted them all.

 

[Sahani]

Yeah, I tried some exotic benzene/pentane dicyclic stuff. I still feel like there's an answer though, just need to have it click. All the odd carbons and oxygens have to fall into place.

 

[Medikit]

Yeah, I tried some exotic benzene/pentane dicyclic stuff. I still feel like there's an answer though, just need to have it click. All the odd carbons and oxygens have to fall into place.

Something doesn't feel right to me.



Arch, was the molecular formula given to you? Was the integration given to you? Or did you determine them experimentally?

 

[Thearchitect]

Something doesn't feel right to me.



Arch, was the molecular formula given to you? Was the integration given to you? Or did you determine them experimentally?

I'm given the formula and the NMR. The NMR is too sloppy to make out, so it has been labeled by someone. They have the integration(not a number, but I measured them with a ruler to double check) and over each blob-looking peak, "two peaks" is written. I'm assuming that means doublet.

 

[CanIMakeIt]

I'm given the formula and the NMR. The NMR is too sloppy to make out, so it has been labeled by someone. They have the integration(not a number, but I measured them with a ruler to double check) and over each blob-looking peak, "two peaks" is written. I'm assuming that means doublet.

Two peaks may not necessarily be doublets ..... could be two singlets ..... just a thought ......

 

[Nuel]

I think I studied elementary NMR theory well, but this question doesn't sound right to me. The doublet of 6H's has to allow some form of molecular symmetry and 3 carbons, 6 protons and 3 oxygens are refusing to do the job on a para-substituted benzene ring. So I think the question is erroneous.

 

[Medikit]

Two peaks may not necessarily be doublets ..... could be two singlets ..... just a thought ......

That actually makes sense.

 

[Nuel]

I think those peaks are singlets. a methyl ether addition and methanol ether moiety--all added para-wise to the Benzene ring.

 

[Thearchitect]

I think those peaks are singlets. a methyl ether addition and methanol ether moiety--all added para-wise to the Benzene ring.

Ah wah? Moiety? This isn't a chemistry thesis.

 

[The Hen]

Ah wah? Moiety? This isn't a chemistry thesis.

If the problem is legit, then there is no way it could have a benzene ring. Think about it. a doublet at 7 and 8 shows 4 H's on the benzene ring. The benzene ring is also para. Then you said there was a doublet that consisted of 6H's. The only way that the 6 H's could be split that way is if a H was next to them. If you add up the H's, you get 4+6+1=11

 

[The Hen]

I think I got it...LOL...I'm such a loser.

CH3-(C=O)-CH=CH-(C=O)-CH=CH-(C=O)-CH3

 

[Medikit]

That would give one singlet with an integration of 3. This is a doublet or two singlets... unless something weird is going on.

 

[The Hen]

That would give one singlet with an integration of 3. This is a doublet or two singlets... unless something weird is going on.

You're right...DO'H..oh well..twas a valiant effort. ...I'm done with ochem and the mcat anyway 😀

 

[ChemMN]

C9H10O3

There is a doublet(2H) at 7, a doubet(2H) at 8, and a doublet(6H) at 3.9.

Been staring at this forever. Nothing works to give that NMR. I think the question is BS.

I've got your answer. The peaks at 3.9 are not part of a doublet, they are from two distinct methyl groups. The compound is methyl anisate

CH3-O-(para Benzene)-(C=O)-CH3

 

[ChemMN]

Sorry, it is an ester

CH3-O-(para Benzene)-(C=O)-O-CH3

 

[The Hen]

I've got your answer. The peaks at 3.9 are not part of a doublet, they are from two distinct methyl groups. The compound is methyl anisate

CH3-O-(para Benzene)-(C=O)-CH3

👍

good work

 

[Medikit]

Sorry, it is an ester

CH3-O-(para Benzene)-(C=O)-O-CH3

You win the thread

 

[The Hen]

You win the thread

I havent had ochem in about 2 years now, so bare with me. Doesn't the graph tell you if the H's are on separate methyl groups? Wouldn't it have said 1H and 1H rather than 2H?

 

[ChemMN]

I havent had ochem in about 2 years now, so bare with me. Doesn't the graph tell you if the H's are on separate methyl groups? Wouldn't it have said 1H and 1H rather than 2H?

This is a common misconception that many people have about NMR. When you get a spectrum, all you see is peaks. You do the integration yourself, so the spectrum cannot tell you where protons reside on a molecule. By the way, questions like this are stupid. A chemist would know what he/she was trying to synthesize (much more info than just the formula), so it is usually a lot easier to decipher an NMR spectrum.

 

[The Hen]

This is a common misconception that many people have about NMR. When you get a spectrum, all you see is peaks. You do the integration yourself, so the spectrum cannot tell you where protons reside on a molecule. By the way, questions like this are stupid. A chemist would know what he/she was trying to synthesize (much more info than just the formula), so it is usually a lot easier to decipher an NMR spectrum.

thx man 👍