NMR Determination of Paramagnetic Susceptibility

The magnetic moment of a nucleus with nuclear spin quantum number /is 

The nuclear moment will interact with a local magnetic induction (flux density)t 5ioc to cause an energy change (Zeeman effect) 

For protons v (Hz) = (4.26 X 10 )5,o(. (tesla), so that, for typical fields of 1 to 5 T, falls in the radio-frequency region. In practice v is usually fixed at some convenient value (e.g., 60, 100, or 220 MHz) and the induction 5 is varied until resonance is achieved. 

Energy levels, allowed transitions, and spectrum of a nucleus with / = f in a magnetic induction of magnitude B. 

In general, the local induction at the nucleus will differ from the externally applied 

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Determinations of epr fine structure and paramagnetic susceptibilities are most often used. For characterization of higher spin orders, neutron diffraction and other physical methods may be useful. On the other hand, a successful measurement of normal high-resolution nmr spectra would serve as good evidence for singlet ground states of the chemical entities at issue. 

Magnetic susceptibilities of solutions — These are useful parameters for determining equilibrium constants for reactions involving spin changes. The Evans nmr method utilizes the observed shift in the resonance line (say of a proton of t-BuOH or hexamethyldisilox-ane) in solution when a paramagnetic substance is added. The paramagnetic shift A/ is related to the magnetic moment (jj, of the solution at TK by the approximate expression... 

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