Molecular motion in succinonitrile and malononitrile by nuclear magnetic resonance

Abstract

Measurements are reported of the proton spin-lattice relaxation time, T1, at 21 "5 and 14"3 MHZ and the relaxation time in the rotating frame, Tip, at 14" 3 MHZ for HI = 7" 1 G, in liquid and solid polycrystalline succinonitrile, (CH2CN)2. Correlation times for molecular reorientation and diffusion have been obtained. In the liquid these agree with dielectric correlation times. In the upper temperature solid phase I, the N.M.R. reorientational correlational time has an Arrhenius behaviour with an activation energy greater than in the liquid and only agrees with the dielectric correlation time at lower temperatures. Reasons for the discrepancy at higher temperatures are discussed and an anomaly pointed out by Clemett and Davies [10] is resolved. At higher temperatures in phase I, Tip is controlled by translational diffusion modulated interactions, as also, possibly, is T1 just below the triple point. Values for the translational correlation time are obtained. It seems possible that a 'defect diffusion' mechanism [24] is active in this substance rather than the lattice diffusion usually accepted in plastic crystals with simpler globular molecules. It is confirmed that no large scale molecular motion occurs in the lower temperature phase II.It has been shown that malononitrile, CH2(CN)~, does not have a plasticcrystal phase.

13C spin-lattice relaxation in rotationally disordered solids

“…A point for general emphasis is that obtaining rotational correlation times over the complete temperature range of solid I succinonitrile via aaC-H intramolecular dipolar spin-lattice relaxation measurements was relatively straightforward ; in contrast to proton-proton relaxation [3,4], which is complicated by admixture of intra and intermolecular effects, and 14N quadrupolar relaxation, for which the observable linewidths limited the temperature range available for study. The 13C technique might thus appear to be superior to those of 1H and 14N, but this must be qualified by the fact that they each monitor the rotations of different vectors, so are complementary.…”

“…Downloaded by [Nanyang Technological University] at 04: 16 17 June 2016 phase (solid II) to solid I cannot be attributed to simple rotation about the central C-C bond. Proton spin-lattice relaxation times have been measured for liquid and solid (polycrystalline) succinonitrile by Powles et al [4]. Their Tl's are discontinuous across the melting-point and linear on a logarithmic scale against l/T, with activation energies of 3.6 kcal/mole (liquid) and 6-0 kcal/mole (solid I)J-.…”

Molecular motion in the plastic phase of pivalic acid studied by nuclear magnetic resonance

“…The Tip and T2 results for tile methyl protons presented in figure 1 are therefore interpreted in terms of this mechanism. Use of a weak collision theory [10,11] with correlation functions appropriate to a random walk model [12] with average molecular jump time T gives the following expressions for Tip [13] and T2 [14].…”

On self-diffusion in plastic crystals

“…These latter theories do not yield such a consistent fit to all Similar analyses have been applied to data on three other (powdered) organic plastic crystals, norbornylene [16], cyclohexane [17] and succinonitrile [18,19], for which detailed and reliable N.M.R. relaxation and complementary radiotracer data exist.…”