Nmr

[SunChip]

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When comparing the NMR spectrum of ethanol to the NMR spectrum of anhydrous ethanol, why are their additional lines that appear in the spectrum of anhydrous CH3CH2OH? Why does the -OH signal itself appear as a triplet? Thanks in advance!

 

[Cool Beans]

When comparing the NMR spectrum of ethanol to the NMR spectrum of anhydrous ethanol, why are their additional lines that appear in the spectrum of anhydrous CH3CH2OH? Why does the -OH signal itself appear as a triplet? Thanks in advance!

You'll almost never see a 'clean' spectrum for ethanol in an instructional class. In a 'clean' sample the hydroxyl hydrogen as two neighbors from the adjacent CH2 group. However for most alcohols, the OH hydrogen will appear as a broad singlet due to what's called 'fast proton transfer.' The OH hydrogen is being exchanged with impurities (usually water) in the sample. As such, we visualize a broad range of environments in the solution as it's being exchanged. Long story short, this is what leads to the broad singlet usually visualized when the sample isn't 'clean.'

Hope this helps.