Nuclear Overhauser Effect (NOE): The purpose of proton decoupling is to eliminate overlapping signal patterns and to increase the signal to noise ratio. Decoupling of the protons increases the signal to noise ratio by causing the collapse of quartets, triplets, and doublets to singlets and by causing a favorable increase in the number of carbons in the a-spin state relative to the -spin state. The latter effect is called the Nuclear Overhauser Effect (NOE); how it causes this change in spin state populations will not be discussed here.

Discussed in the Coupling (carbon) section.