Group 1 - Exchangeables and Aldehydes

The origin of this unpredictability lies in the fact that they are relatively acidic, and can undergo exchange in solution. The appearance of the signals we observe is governed by the rate at which this process occurs, the rate being greatly influenced by the nature of the solvent, its water content, pH, temperature, and concentration of the compound. 

Alkyl-OH 5-1 Can appear sharp and are capable of coupling to adjacent protons in dry aprotic solvents. Easily exchanged by shaking with D20. 

Phenolic-OH (H-bonded) 17-11 Can be broad but more usually sharp as proton exchange is slowed by need to break both bonds. Can therefore be more difficult exchange. Warm if necessary. 

Alkyl-COOH 12-6 Usually broad but can be extremely broad Very easily exchanged. 

Alkyl-NH2/NHR 5-1 Generally similar to alkyl-OH but maybe somewhat broader even in dry solutions and less likely to couple to adjacent protons. Ability to protonate nitrogen tends to broaden protons and displace to lower field. Easily exchanged. 

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