o-chem MNR help and tips?

[eddie269]

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Hi guys. I have NEVER been good at MNR. I am taking ochem 118c (last chem class!) and I have another midterm tomorrow. I never seem to get MNR's correct. I went to office hours for every professor I had and some TA's. they all had different ways.

Well, heres my current way of doing things. any help, pointers, tips would be great.

1- degrees of unsaturation: for dbl. bonds, or ring structure

2-peaks on H-NMR graph: to see neighboring protons (n+1), how many protons in that area, types pf protons.

3- IR: to see functional groups.

4-I also think of the main topics I am doing (i.e. mostly amines and nitriles in these chapters so NMR should reflect that)

By now, I usually have a few pieces here and there, but here are usually a few pieces missing. So I guess and put them together but I NEVER get full credit cause my final answer is always off. It's been a frustrating year with NMR spectrums with the countless midterm and finals I took, I only got full credit for one NMR problem.

anyone who is an expert who has tips?

 

[bananaface]

It might help you to make flashcards. You could put a functional group on one side and the characteristics of the spectrum it produces on the other. You need to know the size of the peaks expected, how many peaks, and where the peaks will be seen. You just have to memorize every group. Looking through a bunch of spectra examples can help solidify what the peak for a particular functional group looks like. You also need to know what regions noise usually falls in, so you can disregard it. If it's not noise, you need to figure out what it is to get a complete answer. Knowing where to expect each group and practicing will make you feel alot more confident about your NMR interpreting skills.

Remember the old adage: "Be it near, be it far, nothing sucks like NMR"

 

[young skywalker]

Interpreting NMR data is usually a matter of practice.
Make sure you have this paper
J. Org. Chem. 1997, 62, 7512-7515
NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities
Make sure you have a Mass Spec, very important for determining the purity, and confirming the identity of your compound. (Since other impurities can give you crap)
Other than that its just practice practice practice..

 

[OSURxgirl]

I agree with skywalker. The only way I mastered these problems was by doing them again and again and again. It's hard work, but after awhile, it all starts to fit together. Ultimately, I ended up liking spectroscopy because I enjoy puzzles. It helps to always write down what you DO know, and use that to eliminate things. Then, take the possibilities that are left and pick the one that's most reasonable. Best of luck on your exam.