Silicon compounds, organic tetramethylsilane

Tetramethylsilane (TMS) is referred as the standard because of the low electronegativity of silicon, the shielding of equivalent protons in tetramethylsilane is greater than most of the organic compounds. Therefore, the NMR signal for a particular proton in a molecule will appear at different field strengths compared with a signal for TMS ... 

The compound we use as a reference sample is usually tetramethylsilane, TMS. This is silane (SiH with each of the hydrogen atoms replaced by methyl groups to give Si(CH3)4- The four carbon atoms attached to silicon are all equivalent and, because silicon is more electropositive than carbon, are fairly electron-rich (or shielded), which means they resonate at a frequency a little less than that of most organic compounds. This is useful because it means our reference sample is not bang in the middle of our spectrum ... 

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