HNMR solvents

[donaldduck]

why is it that when CDCl3 is used as a solvent in HNMR instead of D20 we would get a different amount of signals. Also, what type of hydrogen ,if any, does this difference in signals represent? (i.e.: is the hydrogen acidic, does it belong to a double bond, etc...)

Thanks!

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[orgohacks]

why is it that when CDCl3 is used as a solvent in HNMR instead of D20 we would get a different amount of signals. Also, what type of hydrogen ,if any, does this difference in signals represent? (i.e.: is the hydrogen acidic, does it belong to a double bond, etc...)

Thanks!

Alcohols, carboxylic acids, and amides each have hydrogens that undergo rapid exchange with water. In D2O the H on these molecules gets swapped for D, so that the peak becomes "invisible" in NMR. In CDCl3 this doesn't happen, so you can see the signals corresponding to those functional groups.
Hope this answers your question - James

 

[loveoforganic]

Another common reason is the chosen solvent masks your peaks