[pecan66]

Dear All,

I would like some help with explaining the coupling in the spectrum of bromobenzene.

So from what I can see there should be three peaks corresponding to the three different proton environments.

Proton A (ortho to bromine) would couple to proton B (meta to Br) to produce a doublet and would then couple to proton C (Para to Br) via W coupling to produce a doublet of doublets. However looking at the spectrum there is a doublet but it has a complicated splitting pattern and I still can't explain its multiplicity even when para coupling is considered. The peaks for proton B and C are even more complicated.

I've provided a link to the spectrum (It's on page 3 of the doc)

Could anyone explain how the spectrum gets it's appearance?

Thanks



http://www.unm.edu/~orgchem/304L%20pages/08%20Lab%201e%20Aromatics.pdf

[Babcock_Hall]

Compounds such as this one do not follow the simple first-order rules that are taught during one's sophomore year.  What level of class is this?  Did your instructor introduce the concept of magnetic equivalence?

[OrgXemProf]

First, a reference to the concepts of "magnetic equivalence" and "higher order spin systems"; see: http://www.chem.wisc.edu/areas/reich/nmr/05-hmr-07-pople.htm

Next: The proton NMR spectrum of bromobenzene offers a tightly-coupled AA'BB'C spectrum. An analysis of this complex spin system, found in the proton NMR spectrum of phenol and thiophenol, appears in the following publication:

Glidewll, C.; Rankin, D. W. H.; Sheldrick, G. M. Trans. Farady Soc. 1969, 65, 2801-2805.

If only life were first-order, how simple it all would be.