ISSN:
0749-1581
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The diamagnetic and paramagnetic terms of the 29Si nuclear shielding constant of silatranes, XSi(OCH2CH2)3N, and the related four-coordinated silicon compounds, triethoxysilanes, XSi(OC2H5)3, have been estimated to explain the experimental peculiarities of their 29Si NMR spectra. High-field shifts of the 29Si NMR signals of silatranes relative to triethoxysilanes are of diamagnetic origin, arising mainly from the existence of the Si←N bond and pentacoordination of the silicon atom in silatranes. At the same time, the decrease in the positive charge on the silicon atom upon Si←N interaction increases the absolute value of the negative paramagnetic term. When the Si←N bond in silatrane molecules becomes stronger through introduction of a more electronegative substituent X, the absolute value of the difference in the paramagnetic terms between silatranes and the related triethoxysilanes increases to a greater extent than that in the diamagnetic terms. This reduces the difference in 29Si chemical shifts of the corresponding four- and five-coordinated silicon compounds with increasing electronegativity of the substituent X.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260230702
