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The calculation of the nuclear-magnetic-resonance spin–lattice relaxation time has been extended to include molecules which approximate an axially symmetric ellipsoid and have internal motion about an axis at any constant angle to the symmetry axis of the ellipsoid. The calculation is carried out explicitly for two models of internal motion. These are, random reorientation among three equivalent positions 120° apart, and rotational diffusion.

Doublet splitting in the NMR spectrum of montmorillonite clay–water systems arises from the preferred orientation of water molecules on clay gels. The small magnitude of the doublet splitting compared to that expected for motionless molecules indicates dynamic preferential orientation of the water in the clay–water systems. The fact that the doublet splitting is observed for the D2O–clay gels at all temperatures but only for the H2O–clay gels at low temperatures and relatively small water content suggests the importance of hydrogen exchange in the observation of the H2O doublet. Hydrogen exchange “washes out” the proton doublet but not the deuteron doublet. The reason for this is the difference in the proton and deuteron nuclear spin interactions which give rise to the doublet.

Studies of the nitrogen, deuteron and proton relaxation rates of liquid acetonitrile at various temperatures were carried out by pulsed N.M.R. techniques. Re-orientation of the methyl group about its symmetry axis is found to be approximately ten times faster than the re-orientation of the nitrile group. Analysis of the data provides an example of a large roomtemperature contribution to the intramolecular relaxation component by a spin-rotation interaction. Previously sizeable spin-rotation interactions were considered to be insignificant for organic molecules at room temperature.

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