Nuclear - Overhauser Effect
Energy scheme for 2-spin system with Jax = 0
The NOE creates non-equilibrium state of the molecule !
1. A is saturated by radiation energy
2. By this the system is inverted
3. 'Normal’ transfer is no longer observed
Signal intensity = prop. to difference in occupation of both levels
Thus: = After saturating all A transfers only X is observed ( N1-N2 und N3-N4)
--> if Wo is preferred --> negative NOE (macro molecules)
--> if W2 is preferred --> positive NOE (small molecules)
Quantum mechanics :
W1 = 1 – Quanten transfer,...
W1 processes allowed in excitation, W0 und W2 forbidden
W1, W2 and W0 processes in relaxation allowed