Why Don Protons on Oxygen Split Adjacent Hydrogens?
Under normal conditions for NMR spectra acquisition, no coupling is observed between the hydroxyl hydrogen and hydrogens on the carbon atom to which the hydroxyl group is attached. A typical alcohol undergoes intermolecular proton exchange at a rate of 105 protons per second. This means that the average time of residence of a proton on oxygen is 10-5 seconds. About 10-2 to 10-3 second is required for an NMR transition event to occur and be recorded. As far as the NMR spectrometer is concerned, the hydroxyl proton is unattached more frequently than it is attached to oxygen, and the spin interaction between the hydroxyl proton and any other proton in the molecule is effectively decoupled. Rapid chemical exchange decouples spin interactions, and the NMR spectrometer records only the average environment it senses for the exchanging proton. To observe coupling between hydroxyl protons and other protons in the molecule, the temperature of the experiment can be reduced. This will slow down th
