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Protons in the NMR


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#21 Gamma Girl

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Posted 11 December 2016 - 01:02 PM

The answer key says the red hydrogen sees 3 peaks. How is that?


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#22 hypervalent_iodine

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Posted 12 December 2016 - 09:46 AM

Because that hydrogen is electronically equivalent to the other hydrogen attached to it and to the CH2 to the left. It won't couple to the CH2 side on the left due to this, but it will couple to the other CH2. This means n = 2, so you get a triplet.
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#23 Fuzzwood

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Posted 12 December 2016 - 02:29 PM

The opposing CH2Cl site is too far away to really influence coupling, if that would confuse you otherwise. If it would be right next to it (1,3 dichloropropane instead of the current 1,4 dichlorobutane), it would cause a 5-fold splitting.


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#24 BabcockHall

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Posted 12 December 2016 - 04:31 PM

addendum: doublet from structure 1 is from t-butyl 


No, the H's would not couple.  n is 1 due to the t-butyl because the distance is 2 bonds.


Explain structure 3 to me, please.

 

Between the hydrogen atoms of the t-butyl group and the hydrogen in question there are four bonds, not two bonds.  When there are four bonds, the coupling constant is usually small and may be undetectable.


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