ISSN:
0749-1581
Keywords:
13C NMR
;
Spin-lattice relaxation data
;
Tropine
;
Pseudotropine
;
Rotational diffusion
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Models for isotropic, axially symmetric and fully anisotropic overall rotational diffusion with single diffusional or three-state internal motion are reviewed or derived and applied to 13C spin-lattice relaxation data for the N-methyl groups of tropine and pseudotropine. The results are compared. Complete equations containing the dependence on the equilibrium positions are given for the three-state jump models. Despite the considerable approximations which these models imply, they are able to predict the expected features of the internal N-methyl group motion in tropine and pseudotropine: hindered three-state jumping, which is of the same rate for tropine and pseudotropine and which is moderately independent of concentration and the model for overall motion. Although the nitrogen inversion in these compounds is slow compared with methyl rotation, and does not affect the relaxation, the equations are also derived for double internal motion where the internal rotation axis jumps between two non-equivalent sites having an arbitrary but fixed orientation within the molecule, and where the innermost internal motion is diffusional or jumpwise as in single internal motion. Some considerations regarding the units of the rotational diffusion constants, errors in T1 measurements, and the reduction of the equations for fully anisotropic overall motion to equations for axially symmetric and, further, for isotropic overall motion are presented.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260241208
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