Molecular Motion in Phenpropylammonium Chloride Studied by Deuterium NMR

Abstract

Abstract Cation dynamics in phenpropylammonium chloride, C6H5(CH2)3NH3Cr, were studied in three different solid phases by means of 2H nmr. Both 2H nmr line shapes and spin-lattice relaxation studies were performed on the ammonium head group, the adjacent methylene group and the phenyl-ring. In the low temperature phase, solid III, the - ND3 group dynamics were dominated by C3 jumps about the C - N axis. From the observed minima in T1Z and T1Q a quadrupole coupling constant of 165 ± 5 kHz was obtained. The 2H nmr line shapes of the methylene group indicate that this group does not execute any large amplitude motion in the low temperature phase. In contrast, the phenyl ring deuterium nuclei give rise to line shapes characteristic of C2 ring flips about the Cpara - Cipso axis. In the solid II phase the 2H nmr line shapes of both the - ND3 and - CD2 - groups are characterized by asymmetric Pake powder patterns. Since one of the principal components of the electric field gradient tensor remains temperature independent for both groups, it was concluded that these groups perform planar large-amplitude motions between two sites. Axially symmetric spectra were obtained for all three groups in the high temperature phase, solid I. The 2H nmr line shapes indicate the presence of whole ion reorientation about a molecular axis. In addition, the - ND3 groups perform C3 jumps about the C - N axis and the - C6D5 group display line shapes characteristic for rotational diffusion about the Cpara - Cipso axis.