Physical properties of spin labels

In this section we consider intramolecular magnetic interactions, relaxation times, and intramolecular motional modes. 

Intramolecular magnetic interactions in nitroxides are (1) the nitrogen hyperfine tensor (2) the g tensor (3) methyl proton hyperfine tensors (4) other proton hyperfine tensors (S) the nitrogen quadrupole coupling and (6) couplings to trace isotopes, mostly One desires to know how these properties depend on solvent and 

Nitroxide relaxation times include (1) the electron spin lattice or longitudinal relaxation time, Tj (2) the electron spin-spin or transverse relaxation time, T2 (3) the 

Possible intramolecular motional modes that might in principle affect the magnetic parameters and relaxation times are (1) methyl group rotation (2) interconversion of axial and equatorial methyls (3) inversion of the NO bond with respect to the CNC plane (4) interconversion of five-membered rings between twisted and planar conformations and (5) other ring motions that may exist. 

Available information on these physical parameters is summarized below. It will become apparent that major gaps in this information exist. The reader is referred to the books on Spin Labels edited by Berliner [22] for background. Forrester s 874-page tabulation of nitroxide magnetic data is an important contribution [31]. 

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