Question

How do you interpret an NMR spectrum?

What do the peaks represent? What different things affect the nature and positioning of the peaks (splitting, height, chemical shift, etc), and how do you interpret that into different elements/compounds etc?
Working in H1 spectra.
Thanks :)

Answer 1

Correctly....

Explanation:

See this old answer....

Any set of protons that can be interchanged by symmetry in a molecule are said to be to be chemically equivalent. And thus they give rise to ONE set of absorptions in the `""^1H` `"NMR spectrum"`. How does this help? Well you got to look at your molecule, and identify the number of chemically equivalent, versus non-equivalent protons you have...

So let us take ethane...`H_3C-CH_3`...the protons are chemically equivalent in that they are interchanged by symmetry. So we observe ONE signal.

And now go to propane... `H_3C-CH_2-CH_3`..the methylene protons are chemically non-equivalent to the flanking methyl groups. And so we should see TWO signals (forget about coupling for the moment). And not only should there be TWO signals, it is a fundamental, underlying principle of all spectroscopy that the intensity of the signals you see, the STRENGTH of the absorptions, is directly proportional to the number of absorbing species... And so in the proton spectrum we should see TWO signal in a `6:2` ratio...

The integration has not been performed here, BUT INTEGRATION should be the first thing you should do to assign the spectrum.

What about `"n-butane"`? Two signals again in a `6:4` ratio. And we go to `"pentane"`....`H_3C-CH_2CH_2CH_2CH_3`...THREE signals in a `6:4:2` ratio, and this is directly revealed by integration.

And so take the molecule you analyze. and predict the number of chemically equivalent protons....

So try this one....for `"neopentane"`, `C(CH_3)_4`, how many signals should you see in the `""^1H` `"NMR spectrum"`? And how many carbon signals in the `""^13C{""^1H}` `"NMR spectrum"`?