Relaxation by Spin Rotation SR Mechanism

4 Relaxation by Jnternuclear Dipole-Dipole Interaction (DD Mechanism) 

If 13C relaxation proceeds exclusively by the DD mechanism, the NOE factor tjc, indicating the enhancement of the 13C signal intensity on decoupling, is determined by the gyromagnetic Tatios of H and 13C according to eq. (3.IS) [34]  

NOE factors of this magnitude are indeed measured for numerous 13C signals of organic molecules, especially for signals of CH and CH2 carbon atoms, as shown for formic acid in Fig. 2.20 [33], 

NOE factors smaller than 1.988 indicate participation of other mechanisms in the spin-lattice relaxation of protonated 13C nuclei. The percentange contribution of the DD mechanism can be ascertained from the measured NOE factor according to eq. (3.19)  

Accordingly, the time constant 7] (DD) of the DD mechanism can be calculated from the measured rjc and l values [eq. (3.20)]  

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