NationStates Jolt Archive

I've completely forgotten what everything means. If I remember correctly, the groupings have to do with the different environments (ie- a triplet has three environments), and that the number of hydrogens is one minus the integral. I'm not sure if this is right, but I need to write my lab report and the people who know this stuff have vanished.

I've completely forgotten what everything means. If I remember correctly, the groupings have to do with the different environments (ie- a triplet has three environments), and that the number of hydrogens is one minus the integral. I'm not sure if this is right, but I need to write my lab report and the people who know this stuff have vanished.
h
WIYF. (http://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_spectroscopy)

Well that question depends on your intelligence levels, obviously if you are too dumb to understand it, it couldn't be explained to you very well, if at all.
*nods*

No.

h
WIYF. (http://en.wikipedia.org/wiki/Nuclear_magnetic_resonance_spectroscopy)

Sifting through it, with minimal success.

a triplet has three environments

A triplet is caused when a group in one environment is attached to a carbon attached to a carbon with 2 protons in a different environment.

It's splitting caused by adjacent environments.

Just to let you know.

A triplet is caused when a group in one environment is attached to a carbon attached to a carbon with 2 protons in a different environment.

It's splitting caused by adjacent environments.

Just to let you know.

thanks.

The splitting and multiplet thing is essentially:

protons (or hydrogens) in one environment show up as split (n+1) times on the graph, where n is the number of protons in seperate environments on an adjacent carbon.

1 hydrogen on adjacent hydrogen - 2 peaks
2 - 3 peaks
3 - 4 peaks
4 (2 carbons adjacent) - 5 peaks.

Depending on the level (A-Level especially), an exam board is unlikely to give you anything with 5 or more peaks from what I've seen.

http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/nmr/nmr1.htm

How it works:
NMR can be done with a nucleus with an odd number of protons + neutrons. The reason for this is that the process depends on the magnetic spin of the nucleus. The substance you are trying to analyze is put in a 'carrier'. Usually, this is D2O... heavy water. Deuterium won't show up in an H-NMR, so it's a good choice. The substance is then placed in a strong magnetic field. This magnetic field will align the spins of the nuclei. Another magnetic field is then used to perturb that alignment. The response is recorded.

You probably don't need to know how it works exactly.

How to read it:
This is the important part.
It sounds like you are talking about 1-D H-NMR. In this kind, you just use one pulse and record the response.

The response depends on how much the electrons shield the nucleus. A proton bonded to a strongly electronegative atom like oxygen will show a greater shift than hydrogens attached to a carbon.

The number of different peaks on the NMR indicates the number of different 'environments'. A molecule with symmetry in some places can have more than one proton in the same environment.

Peak splitting is really not all that useful. Basically, a peak will split when an adjacent carbon also has hydrogens attatched to it. You'll get N+1 peaks, where N is the number of adjacent hydrogens with the same environment. The problem is when you have adjacent hydrogens with different environments. Each environment will contribute N+1 peaks, where N is the number of adjacent hydrogens in that environment. Unfortunately, some of the peaks may overlap, and some might not. Let's say you've got 2 adjacent with 1 environment, and 2 adjacent with another. If none of the peaks overlap, you'll get 6 peaks. If one overlaps, you'll get 5. If two overlap, you get 4.

This problem can be solved by using 2-D NMR. In this technique, a second pulse is used to perturb the spin after a small period of time. The changes in response can be used to plot proton-proton interactions. The resulting graph will show spots on the diagonal where all of the peaks are. Instead of splitting, proton-proton interactions show up as off-diagonal peaks. By looking to see where those line up with respect to the diagonal, you can establish the connectivity of the different environments.

Savvy?