NMR spectrum of highly purified ethanol:

However, if the spectrum of highly purified ethanol sample is examined as shown in Figure, the hydroxyl proton signal splits into a triplet due to spin-spin interaction with two methylene protons. Additionally, the multiplicity of methylene protons is also increased; each of four lines gives rise to a doublet due to interaction with the hydroxyl proton. An expanded spectrum within the region of the methylene protons is shown in the inset of Figure.

Figure: NMR spectrum of highly purified ethanol under high resolution

The difference in the multiplicity of hydroxyl proton in pure and acidified alcohol samples can be best explained in terms of chemical exchange. In a given period of time, a single hydroxyl proton may be attached to a number of different ethanol molecules.