CH3 H3C-Si-CH3 Tetramethylsilane CH3 TMS is added to the sample. ● Since silicon is less electronegative than carbon,TMS protons are highly shielded.Signal defined as zero. Organic protons absorb downfield(to the left)of the TMS signal. => Chapter 13 13Chapter 13 13 Tetramethylsilane • TMS is added to the sample. • Since silicon is less electronegative than carbon, TMS protons are highly shielded. Signal defined as zero. • Organic protons absorb downfield (to the left) of the TMS signal. => Si CH3 CH3 CH3 H3C