[kensher]

Hello!
I am struggling with one of my homework assignments.

Assignment
The task is to predict the ¹H-NMR-spectra of the organic compound butane-2,3-diol.

My answer
I would have predicted three main peaks:

– one peak for the CH₃
– one peak for the CH₂
– one peak for the OH connected to the CH₂.

The answer from the textbook (and Pubchem)
I see it as three different peaks because of three different ¹H-enviroments. However, the textbook says it should only give one peak from the CH₃-radicals. The spectra from Pubchem also only display one peak. Why should it only be one peak instead of three?

Link to spectra from Pubchem: https://pubchem.ncbi.nlm.nih.gov/compound/2_3-butanediol#section=1H-NMR-Spectra

[OrganicDan96]

I would definitely expect to see two shifts for the CH and CH3, might not always see the OH, but for the sake of your work I would say that you can see the OH

[Borek]

Where do you see -CH₂- in ?

Spectrum you linked to is incomplete, it is just a most downfield peak, please read the plot description.

[kensher]

Thanks for both your answers!
Sorry, I meant CH, not CH₂.

I also checked the complete spectra now (from SpectraBase), which showed two peaks.
I guess the textbook had it wrong.
Last question, why don't you always see the OH?

[OrganicDan96]

Last question, why don't you always see the OH?

they are normally broad and sometimes they are so broader that they get lost on the baseline, this i believe is due to hydrogen bonding, it's concentration and solvent dependant, this also gives them unreliable chemical shifts.

They can also exchange with deuterium, depending on the solvent

[kensher]

Thank you!
I appreciate both of you taking time to answer my questions.