Molecular Motion in Phenpropylammonium Chloride Studied by Deuterium NMR

Abstract

Cation dynamics in phenpropylammonium chloride, C 6 H 5 (CH 2 ) 3 NH 3 Cr, 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 -ND 3 group dynamics were dominated by C 3 jumps about the C-N axis. From the observed minima in T 1Z and T 1Q 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~C ipso aX * S "In the solid II phase the 2 H nmr line shapes of both the -ND ? and -CD 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 -ND 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 para -C ipso axis.

Solid State Deuteron NMR Studies of Polyamidoamine Dendrimer Salts. 1. Structure and Hydrogen Bonding

“…These quantities can be measured only at very low temperatures for "static" deuterons, whose long relaxation times (g10 s) would imply prohibitively long experiments. On the basis of literature citations for secondary amide 29,30 and static ammonium 27,28,31,32 deuterons and our own measurements at -30 °C, reasonable maximum PAS values for the asymmetry parameters of R 2 ND and R 3 ND + are estimated to be 0.12 and 0.05, respectively. These values depend on the electronic environment around the dendrimer spacer, which we assume to be independent of dendrimer generation.…”

“…Another source of residual asymmetry is unequal populations of the sites defining 3-fold jumps of the ND 3 + group. For two-site (planar) libration of the RND 3 + rotation axis, the observed asymmetry parameter should increase 28 with increasing temperature. Our observation of the opposite tendency rules out this explanation.…”

“…On the basis of literature values of quadrupole coupling parameters for similar materials, [27][28][29][30][31][32] the two widest powder patterns, which are observed for all generations, are assigned to secondary amide and protonated tertiary amine deuterons, respectively. Deuteration of tertiary amine sites was ensured during our preparation procedure by the excess of strong acid and confirmed by measurements conducted on generation 2 dendrimers with counterion substitution.…”

“…eqs 6 and 7). The angle between PAS and molecule-fixed Z axes was assumed to be β MP ) 70.5°, 28 and for each generation χ PAS was fixed at the value derived by applying the planar libration model IV (cf. eq 8) to interior R 3 ND + sites.…”

“…Spectra of all dendrimer generations consist of broad, overlapping powder patterns arising from three types of deuterons in rigid environments, plus two peaks in the center originating from more mobile parts of the sample. Spectral assignments are based on literature values of quadrupole coupling parameters for deuterons bonded to nitrogens in different hybridization states, [27][28][29][30][31][32] confirmed by experiment on the G ) 2 dendrimer in which Clcounterions were substituted with Br -. Data Processing.…”