Rapid Relaxation via the Double Quantum Pathway

In practice, NOE enhancements will vary, with a twofold (200%) signal increase being the theoretical maximum enhancement for observation with decoupling. Other relaxation mechanisms besides that due to the dipolar interaction will diminish the observed enhancement, q. 

Similar calculations can be carried out on other spin systems. The general result for the NOE enhancement q is 

Enhancement, q. Syn. NOE enhancement. The numerical factor by which the integrated intensity of a resonance increases as the result of irradiation of a spin that is nearby in space. For the irradiation of nuclear spins, the upper limit for the observation of a nearby spin is on the order of five angstroms. 

However, the complete cancellation of the NOE is only temporary. Longer correlation times allow the NOE to be observed (this time with an opposite sign). The NOE no-man s-land in the intermediate correlation time range impedes through-space NMR investigations, but we can circumvent this impediment by changing solvent, temperature, and field, or by changing the NMR experiment itself. 

---