Relaxation by Paramagnetic Substances

As we pointed out in Section 4.11, lanthanide shift reagents owe their utility partly to the fact that the electron spin-lattice relaxation time for the lanthanides is very short, so that NMR lines are not exceptionally broad. On the other hand, there are shiftless paramagnetic reagents that shorten both Tx and T2 to a moderate degree without causing contact or pseudocontact shifts. 

Likewise, small concentrations of paramagnetic ions that complex to suitable ligands and exchange rapidly among ligand molecules can dramatically alter the 

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