Experiments for NMR Undergrad Instruction

The following experiments were forwarded by Cathy Lester.
The keto-enol expt. Another good one is the determination of the activation energy of rotation about the amide bode in DMF. You have to have Variable Temp. to do this experiment, but it REALLY drives home the important concepts of dynamic NMR, AND kinetics in general.

I tried to find my "canned" experiment, with all of the writeup, and data processing info in it...but no luck yet.

For now, this is the best I can do:

The methyl resonances of Dimethyl-formamide are two separately resolved singlets at room temperature due to restricted rotation about the C=N bond. The two peaks coalesce at around 150 deg. C. For Very slow exchange, the two methyls (A & B) have two distinct resonances at (vA & vB). In this regime, the residence lifetimes of the methyls (tA and tB) can be considered to be infinity on the NMR timescale. As the Temperature rised, and the exchange rate increases, tA and tB decrease, and the width of the peaks at vA & vB increase, with the half-width inversly proportional the the lifetimes (tA & tB). Of course at higher temps (faster rates of exchange) the two lines coalesce, and eventually the line sharpens to give a single resonance at a frequency = (vA+vB)/2. At the coalescence temperature the lifetime (t) = sqrt(2)/pi (vA-vB), where vA and vB are the separate frequences with no exchange. At this point, the rate constant can be determined, and from that the activation energy for the exchange process can be derived. I've seen this done both using C-13 NMR, and proton NMR. I've personally only done it via proton NMR, but it shouldn't matter.

For a complete writeup of the analysis of the data, and determination of the activation energy for rotation, check one of the following (I tried to double- check the references, but both books are checked out of our library right now):

Coton and Jackman, "Dynamic Nuclear Magnetic Resonance Spectroscopy", Academic Press (1975).
J. Sandstrom, "Dynamic NMR Spectroscopy", Academic Press, (1982).

I once had a copy of a P-Chem. lab text which had the "canned" experiment; however, I can't find it, and I can't remember the authors or anything...not very helpful, I'm afraid.

Richard Showmaker


Another experiment I can think of is: determination of the structure of a compound based on the J(H-C) values. Run a H-NMR on two very similar compounds and determine which is which by calculation of the %s character of the C-H bonds. (%s = J(H-C) * 0.2) (Example compounds: acetone and acetone oxime, or nitromethane and nitrosomethane)

How about measuring the rotational barrier to binaphthol using VT?

Michael Mosher


One experiement that we performed at Rice University was part of the instrumental analysis lab. The students determinationed levels of caffeine and variuos other components of over-the-counter medications like tylenol and vanquish. Really interesting results for those consumers who WANT TO KNOW.
  1. Simply grind and suspend the tablet in a 2:1 mixture of CD3OD:CDCl3 (not sure of first solvent)
  2. let filler settle out and run H-1 NMR on supernate. [D1=5 seconds P1=30 VT=ambi NS=32]
  3. integrate and compare spectra on a light board
The interesting thing about this experiment is that these results can be compared to HPLC and UV experiments run on the same samples. Keep in mind that fresh samples must be used (no greater than 8 hours old) for the analysis since some of the components do degrade quickly.

Alan M. Kook


I use several compounds to teach interpretation I have the following to be very useful.

For basic Shimming we use CHCl3 in Acetone-d6, 0.1% Ethyl-benzene in CDCl3 and 10% Ethyl-benzene in CDCl3 for setting up and calibration of the experiments. This is an often neglected part of teaching NMR techniques.

Coffee with sugar: Is really a good one for learning how to set up a WATERGATE and presaturation experiments. Never add cream to the coffee it really messes the spectra up.

Gamma amino butyric acid: Very useful for teaching COSY interpretation. And 1-D techniques.

Pamoic acid: Useful for the study of NOE's and NOESY interpretation

alpha nathpthol: is an alternative for NOE studies. Not quite as good as Pamoic acid.

Alpha INONONE: great for HETCOR interpretation and DEPT's ( ia have also used Beta INONONE for comparison)

Alpha Santonin: extremely useful in the study of temperature dynamics and COSY interpretation

I have several compounds for multinuclear studies, but I've never had time to teach this course. So I do not know if they are real good for this yet.

I also have several compounds that I will be using later this summer to introduce HMBC's, HMQC's, 3-D's and several real nice gradients experiments that I have worked out.

I usually teach a 4 week course to High school Interns in our labs in Woodlands, Texas during the Summer. I've found that a few compounds such as the ones above are very useful for teaching the basics of experimental technique, and choice as well as interpretation.

If you would like I could send some of the protocols some of the interns have worked out for themselves over the last several summers.

M. Brown


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