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1H NMR OH and NH

Link to video on OH and NH protons in 1H NMR

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OH and NH protons

Protons on oxygen or nitrogen atoms are a little strange. They can show up anywhere between 2-6 ppm. Because protons on OH and NH are involved in hydrogen bonding, their chemical shift can change depending on the temperature and concentration of the solution. They are not always broad peaks. Sometimes they stay on the molecule enough to couple.


Usually, these peaks are broad, hump-like peaks. This is because the hydrogen atom disassociates from the OH or NH bond. It falls off and returns to the molecule, so there usually is not time for it to couple with other protons. 


One laboratory trick to help determine if a 1H NMR peak is from an OH or NH proton is to add D2O, heavy water, to the NMR sample.  D2O interacts with the OH or NH proton and the hydrogen atom and deuterium atoms switch to form O-D or N-D. The 1H NMR peak then disappears confirming OH or NH. Protons on carbon atoms will not trade with deuterium of D2O. A new peak will grow in the spectrum, though. HOD is formed in the reaction.

Ethanol 1H NMR spectrum before and after shaking with D2O

9. The 1H NMR spectrum of isopropanol is below without its scale shown. Based solely on peak splittings and peak shapes, label each peak with the appropriate letter to match the protons associated with each peak.

isopropanol 1H NMR problem

Answers

9.

isopropanol 1H NMR problem answer

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