Silicon NMR on Spinsolve – Part 2

In my last blog post I introduced silicon NMR on Spinsolve and showed a variety of 1D 29Si{1H} and 29Si-1H DEPT spectra. In this post I’m moving on to talk about some 2D experiments that are useful for silicon studies. One of the most useful and widely used of those is the 1H-29Si HMBC experiment, which correlates proton and silicon chemical shifts over two or more chemical bonds. For example, Figure 1 below shows a 1H-29Si HMBC spectrum of the 1,1,3,3,5,5-hexamethyltrisiloxane sample I used before, collected in around 17 minutes. The 1H spectrum is shown along the horizontal axis of the 2D spectrum, and the 29Si spectrum is shown along the vertical axis.

Fig. 1. 1H-29Si HMBC spectrum of 1,1,3,3,5,5-hexamethyltrisiloxane

In the HMBC spectrum we see two-bond correlations between the silicon atoms and the hydrogens of the methyl groups attached to each silicon. The HMBC spectrum makes it clear which signals in the proton spectrum are due to which methyl groups in the molecule.

Another useful 2D experiment for silicon is the 1H-29Si HSQC experiment, which correlates proton and silicon chemical shifts over one chemical bond; in other words, it tells us which silicon atoms are directly attached to hydrogen atoms. Figure 2 below is a phase-sensitive 1H-29Si HSQC spectrum, collected in 35 minutes. In the 2D spectrum we see a single cross-peak indicating a correlation between the hydrogens directly attached to silicon atoms 1 and 5 (green boxes). As we would expect, since there are no hydrogens directly attached to silicon 3 there is no cross-peak associated with that silicon atom.

Fig. 2. 1H-29Si phase-sensitive HSQC spectrum of 1,1,3,3,5,5-hexamethyltrisiloxane

In this short blog post, I’ve shown just a small sample of the 2D spectra I collected on the Spinsolve Silicon system; more spectra covering a range of silicon-containing compounds will be available on the Magritek website very soon. Of course, if you’re interested in the Spinsolve Silicon system and/or have some samples you’d like us to collect data on then let us know!