Identification of a defect chain motion in n-alkanes by means of nuclear magnetic resonance spin–lattice relaxation time measurements

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Abstract
Proton spin–lattice relaxation timemeasurements in the rotating frame as a function of inverse temperature have revealed shallow minima not previously observed for a series of n‐alkanes ranging from n‐C22H46 to n‐C41H84. These minima cannot be interpreted in terms of reorientations of methyl groups or entire chains. The most likely reorientational model is one in which a thermally activated trans–gauche defect motion modulates the internuclear dipolar interactions. The results suggest that the gauche defect equilibrium orientation has a higher energy than that of the ordered all‐trans equilibrium orientation. Activation energies for the motion as well as energy differences between the two orientations have been extracted from the results for these n‐alkanes.