Understanding NMR

[The_Enantiomer]

I'm just finishing up Organic Chemistry 1 this semester. I have a firm grasp on FT-IR Spectroscopy. The spectroscopy problem I have is proton NMR. We have done done work with Carbon13 NMR, and I don't think we will anytime during my undergrad years. I am able to identify peaks within the spectra if I know what the structure is, but what I'm still not sure about is how to identify unknown compounds given the spectra. Does anyone have any tips, I don't have any readily available spectra to show unfortunately. I understand the reactions well enough to know what products should be produced.

 

Any help would be appreciated!

 

-Evan

Edited November 29, 2012 by The_Enantiomer

[RVJ]

HNMR works in a very similar way to Carbon-13 NMR. It tells you how every hydrogen in the molecule is being affected by the other hydrogens in the molecule. For instance, HNMR tells you how many different types of hydrogens you have, and where they're located on the molecule. Take a benzene ring for example,

There is only one peak, because there is only one kind of hydrogen on a benzene ring. You can use HNMR in combination with CNMR and IR, and perhaps UV -- if you have a conjugated compound. I find it most helpful to take every piece of individual information on it's own accord, and write down what each peak of every graph you have available could mean. Once you have done that, look at everything you have written down, and see what fits together.

[BabcockHall]

The chemical shift of each peak tells about the environment of the atom, i.e. what functional group is nearby. The area of the peak is proportional to the the number of equivalent hydrogen atoms. The number of peaks is the number of groups of equivalent hydrogen atoms. If there is symmetry present, this can sometimes be inferred from the number of peaks versus the number of hydrogen atoms in the chemical formula. The splitting pattern gives an indication of the number of neighboring hydrogen atoms.