Proton NMR: pi conjugation & aromatic ring equivalence

[circulus vitios]

First of all

Second of all, is this something we should know for the MCAT? I've literally never heard of pi conjugation negating the equivalence of protons in an aromatic ring. Are there any other obscure "exceptions" that I should know about? I didn't know the MCAT tested on complex splitting, either.

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[Postictal Raiden]

First of all

Second of all, is this something we should know for the MCAT? I've literally never heard of pi conjugation negating the equivalence of protons in an aromatic ring. Are there any other obscure "exceptions" that I should know about? I didn't know the MCAT tested on complex splitting, either.

This question is tricky. My answer was A .

It requires several folds of knowledge in order to answer it (knowing how many non-equivalent hydrogens exist, knowing that the n+1 rule applies only to equivalent hydrogens, and remembering the rules regarding deshielding). I wouldn't expect it to be on the test, but if it were, it is still a fair game.

 

[BestDoctorEver]

I dont see 8 non-equivalent H.....

 

[mcloaf]

I dont see 8 non-equivalent H.....

5 on the ring and 3 on the chain.

The pi conjugation eliminating symmetry seems a little harsh for an MCAT question. I do think you should know the splitting though, as this one is pretty straightforward and definitely something you could see on the test.

 

[Meredith92]

I never knew that the neighbor rule n+1 was only for equivalent hydrogens. Do you mean that neighbors on either side must all be equivalent to each other?? If so, how do you calculate the splitting in that case??