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Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 15, 2018 | https://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch120
Principal Ρ Chemical Shift Tensor Components as Determined by Solid State NMR J. P.
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DUTASTA ,
J . B. R O B E R T , and L. W I E S E N F E L D
Laboratoires de C h i m i e , D é p a r t e m e n t de Recherche Fondamentale, Centre d ' É t u d e s N u c l é a i r e s , 85 X, F.38041 Grenoble C é d e x , France
There exists a fairly large amount of experimental data on the chemical shift of molecules dissolved in isotropic phases. However, one is still far from having a good rationale of the different factors which may influence the phosphorus chemical s h i f t . The same i s true for the other nuclei which may be studied by n.m.r. 31p
The physical reason to this i s that the n.m.r. screening constant σ is the trace of a tensor of which the individual components can only be obtained by recording spectra i n oriented phases. This may be done by dissolving the molecules i n l i q u i d crystals (1)(2)(3), or by performing high-resolution n.m.r. experi ments on powder samples or single crystals (4). The tensor components are expected to be more sensitive to minor structural or chemical changes than their isotropic counterparts (5). We present here some results concerning the determination of the principal values of the tensor by means of a high resolution n.m.r. study i n the solid state. 31p
Experimental. The solid state high resolution n.m.r. spectra were run on a CXP 200 BruKer spectrometer i n which the Ρ nucleus resonates at 81 (1Hz. Samples used were finely powedered and hand-tamped i n glass tubes. The spectra were recorded using the Proton Enhanced Nuclear Induction Technique C_6) on the same basis of a one shot cross polarization and high power decoupling during acquisition. A c a p i l lary tube of trimethylphosphate inserted i n the powder sample i s used as internal reference. 3 1
'Current address: Department of Chemistry, University of California, Los Angeles, CA.
0097-6156/81/0171-05 81$05.00/0 © 1981 American Chemical Society Quin and Verkade; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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PHOSPHORUS CHEMISTRY
Results. The r e s u l t s p r e s e n t e d h e r e c o n c e r n two c l a s s e s o f o r g a n o p h o s p h o r u s m o l e c u l e s d e n o t e d c l a s s a) and c l a s s b ) . I n c l a s s a ) , one considers a s e t of c y c l i c thioxo-phosphonates of d i f f e r e n t s i z e , f i v e t o eight-membered r i n g s _1_, 2, 3^, _4, and i n w h i c h t h e c h e m i c a l e n v i r o n m e n t a t t h e p h o s p h o r u s r e m a i n s t h e same Ck . (7J . 0 \CH f
l
/ M
J
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 15, 2018 | https://pubs.acs.org Publication Date: November 11, 1981 | doi: 10.1021/bk-1981-0171.ch120
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