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Origin of the shielding effect in the 29Si NMR spectra of silatranes

✍ Scribed by V. F. Sidorkin; V. A. Pestunovich; M. G. Voronkov

Publisher
John Wiley and Sons
Year
1985
Tongue
English
Weight
417 KB
Volume
23
Category
Article
ISSN
0749-1581

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✦ Synopsis

The diamagnetic and paramagnetic terms of the "Si nuclear shielding constant of silatranes, XSi(OCH2CHz)& and the related four-coordinated silicon compounds, triethoxysilanes, XSi(OC2H5),, have been estimated to explain the experimental peculiarities of their 29Si NMR spectra. High-field shifts of the %i NMR signals of silatranes relative to triethoxysilanes are of diamagnetic origin, arising mainly from the existence of the S i c N bond and pentamordination of the silicon atom in silatranes. At the same time, the decrease in the positive charge on the silicon atom upon S i c N interaction increases the absolute value of the negative paramagnetic term. When the Sic-N bond in silatrane molecules becomes stronger through introduction of a more electronegative substituent X, the absolute value of the difierence in the paramagnetic terms between silatranes and the related triethoxysganes increases to a greater extent than that in the diamagnetic terms. 'fhis reduces the difference in 29Si chemical shifts of the corresponding four-and five-coordinated silicon compounds with increasing electronegativity of the substituent X.

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