Coupling of Protons to 29Si

The isotope 13C has a natural abundance relative to 12C of 1.1% and a spin number of 1/2. Protons directly attached to 13C are split into a doublet with a large 

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As before, n is the number of protons to which I is coupled. The effect of coupling to additional protons is not totally additive, as is shown by the cos"-1 term which reduces Ed. The derived relationship between enhancement and n is shown in Eq. (4). The theoretical enhancement of 29Si coupled... 

The proton decoupled 29Si spectrum of tetram-ethylsilane (TMS) is shown at the top of Figure 6.9 with the proton coupled spectrum for comparison as an inset. TMS is the obvious choice for a 29Si reference compound and we set it at zero ppm. The proton-coupled spectrum is quite interesting because the 29Si nucleus is coupled to 12 equivalent protons in TMS. First order rules predict a multiplet with 13 peaks. There are 9 peaks clearly visible and 11 with a little imagination we do not see the full 13 peaks because the outer ones are too weak and are lost in the noise. 

These sequences produce enhanced proton decoupled 29Si NMR spectra. Coupled spectra can be measured by the same sequences as described below. For the simple case of one silicon coupled to n equivalent protons, the optimum settings of delays r and A and pulse QO is99,106,107. 

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