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Orgo Chem NMR Advice

Nietzsche

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Heya,

I am currently getting ready for my Orgo. Chem exam and we are covering Grignard/IR/and NMR. Do any you guys have any advice on how to understand NMR a little bit better? I believe I can cover Grignard and IR but NMR is a bit tricky.

There are usually these pretty big problems that involve both 1H NMR and 13C NMR along with IR and we are expected to label a few things like some partial compositions and then figure out the structure. Then basically fragment it. Any advice for this topic would be great, thanks.
 

mbe36

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The biggest clue for me was analyzing what the NMR data does NOT show.

ie Think about what makes each of the answer choices unique. Look to see if the data lacks certain peaks. This is a great way to work up to the right answer.
 
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udlax16

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I'm studying for the same thing right now. My professor gave us sheets about what each range means like for C13NMR, in the range of 160-210 it is going to be either an aldehyde or ketone. Just do a search on google, some stuff should come up. Good luck.
 

chewsnuffles

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The biggest clue for me was analyzing what the NMR data does NOT show.

ie Think about what makes each of the answer choices unique. Look to see if the data lacks certain peaks. This is a great way to work up to the right answer.

yeah, that's probably the best way to think about it

the other thing I'd say you should do is look for symmetry in the potential molecule (in two planes!), or the lack of! You probably havn't taken group theory yet, but you only need the most basic parts of it anyway for what you get in orgo.


Maybe someone has a better way of doing this, but for me I would look at it as: more peaks means less symetrical, and vice versa, which allows you to make a "differential diagnosis" on your molecule, i.e. if you know how heavy your molecule is from mass spec and you are sketching it out based on functional groups from the IR, figure out where the functional groups would have to go for there to be the number of peaks that are there! After that, get critical about the shifts and whether they make sense, and also check the integral too!

This is by no means the best way, but it is the only way I can manage to make sense of those things! I'd be interested in hearing from a few experts on how they do it
 
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MisterPeco

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hmm for ur H and C NMRs do they give you IR too? because if they do I think is a lot easier
but anyways i usually start off with the unsaturation numbers if they give you the molecular formula and is asking you to draw the NMR structure

then i start finding the peaks/groups that the NMR is showing and start eliminating the sat. # if it has a double bond or ring or what not
then just keep going from there

NMR is like a puzzle... each peaks represent a diff piece and you just have to find the right order to put them together
 

chemolupusMD

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keep an eye on the specific functional groups, if ur teacher wants to make the test hard, they will try to make it tricky by adding different functional groups in a way that my affect the data. for instance, remember that ketones do not appear in H NMR, so look at ur IR or C NMR for it.
 
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