Nietzsche

10+ Year Member
May 16, 2007
43
0
Status
Pre-Medical
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.
 

WeAreNotRobots

doctor of medicine
10+ Year Member
Nov 11, 2008
1,062
45
u.s.a.
Status
Resident [Any Field]
go to class. review notes. seek help from a fellow student or tutor. read the book.
 

mbe36

10+ Year Member
5+ Year Member
May 15, 2007
952
6
Status
Medical Student
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.
 
About the Ads

udlax16

^lax=lacrosse
10+ Year Member
Jun 10, 2008
43
0
Status
Pre-Medical
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

is a series of tubes
10+ Year Member
Apr 9, 2006
456
1
Seattle, WA
Status
Pre-Medical
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
 
Last edited:

MisterPeco

10+ Year Member
Nov 14, 2008
12
0
Status
Pre-Medical
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
 

RUc10

10+ Year Member
5+ Year Member
Apr 19, 2008
212
1
NJ
Status
Pre-Medical
NMR is like a puzzle... each peaks represent a diff piece and you just have to find the right order to put them together
I thought I had it but it somewhat killed me on my last exam. I could get all the "small pieces" by analyzing the peaks but I couldn't put it together for some reason.
 

chemolupusMD

10+ Year Member
7+ Year Member
Feb 14, 2007
431
0
Houston
Status
Resident [Any Field]
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.
 

link2swim06

10+ Year Member
Dec 14, 2007
3,278
795
Status
Attending Physician
Do problems, more problems, and more problems. I succeed with NMR becuase I did all the book problems twice.
 
About the Ads