Publisher Summary This chapter focuses on Silicon-29( 29 Si) nuclear magnetic resonance (NMR) spectroscopy One nucleus that has become increasingly important from an NMR point of view is 29 Si Silanes are important to the chemical industry as catalysts or additives in catalyst systems New and better ways to characterize these compounds are urgently needed The Silicon-29 ( 29 Si) isotope is a very difficult nucleus to observe because of its low natural abundance (47 %) and low NMR sensitivity at constant field (784 x 10 -3 ) relative to 1 H This chapter includes compounds of general structure (R 3 - n SiO n ) x , where n > 0, x > 2, and R = alkyl, aryl, or H Silicates and extravalent silicon compounds are described The spectral dispersion for organosilicones may be considerable for certain families of compounds The first, 29 Si NMR results reported on polydimethylsiloxanes showed that individual resonance lines can be found for each different silicon nucleus up to a ten-unit oligomer, surpassing the structural resolution achieved by I3 C and 1 H NMR on the same materials

Silicon-29 NMR Spectroscopy

Although it was shown very early [1] that the isotope 29Si is very valuable for NMR research, severe technical difficulties had to be overcome before silicon spectra could be recorded. This was due to the low sensitivity of the isotope resulting from its low gyromagnetic ratio, its low abundance and the rather long relaxation times. The introduction of the Fourier-Transform-Technique (FT-NMR) helped to surmount most of these problems, with the result, that more and more papers concerning silicon NMR appear. Thus, it seems now that most of the salient features of 29Si-NMR are known today

29Si-NMR Spectroscopic Results

Publisher Summary This chapter deals with the recent advances made in silicon–29 nuclear magnetic resonance (NMR) spectroscopy. The tremendous growth of 29 Si NMR has been due largely to the development and application of the pulsed Fourier transform (FT) method in commercial spectrometers. More recently, better sensitivity and the availability of high resolution solids capability on newer spectrometers have further increased the scope of 29 Si NMR. The importance of silicon containing materials to electronics and chemical industries in the form of substrates, catalysts, adhesives, rubbers, fillers, additives, and consumer products has necessitated the development of better characterization methods. For theoretical chemists and physicists, 29 Si chemical shifts, couplings, and relaxation data provide information about bonding, molecular interactions, and motions. Silicon lies immediately below the well-understood carbon and at the beginning of the heavier elements in the periodic table, therefore, understanding the factors involved in determining its chemical shifts and couplings plays a significant role in the development of a unified theory. The chapter presents the more recently obtained results in 29 Si NMR spectroscopy.

M.A. Jensen

Papers

The prediction of 29SiH and 13CH coupling constants in substituted silanes and methanes