Alcohol NMR

2-methyl-1-propanol

C-OH: O.5 - 5 ppm

CH-OH: 3.2 - 3.8 ppm

The OH proton shift is very variable. It depends on the degree of both hydrogen bonding and the rate of exchange with other protons in the solution. These two factors depends on temperature, concentration, solvent, presence of water, or presence of acid impurities. These effects can also broaden the peak.

CH-OH has a coupling constant of about 5 hz. But this is rarely observed, due to rapid exchange with other protons in the solution, such as trace quantities of water. The coupling can only be seen in very pure samples. For example, freshly distilled alcohol, or alcohol from a previously unopened commercial bottle.

The rapid exchange of an alcohol proton with solvents can be used to identify an OH peak. If D₂O  is placed in the NMR tube, deuterium will exchange with the protons, and the OH peak will reduce or disappear after a few minutes.