Molecular Motion in Phenpropylammonium Chloride Studied by Deuterium NMR

Cation dynamics in phenpropylammonium chloride, C 6 H 5 ( C H 2 ) 3 N H 3 C r , were studied in three different solid phases by means of 2 H nmr. Both 2 H 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 N D 3 group dynamics were dominated by C 3 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 2 H 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 C 2 ring flips about the Cpara~Cipso *" In the solid II phase the 2 H nmr line shapes of both the N D ? and C D 2 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 2 H nmr line shapes indicate the presence of whole ion reorientation about a molecular axis. In addition, the N D 3 groups perform C 3 jumps about the C N axis and the C 6 D 5 group display line shapes characteristic for rotational diffusion about the C p a r a -C i p s o axis.