Tetramethylsilane (TMS) is widely used as an internal reference standard in both 1H^1\text{H}1H and 13C^{13}\text{C}13C NMR spectroscopy. Which statement correctly explains a chemical or physical property of TMS that makes it suitable for this purpose?
Silicon is less electronegative than carbon, which increases electron density around the protons and carbon nuclei, shielding them and positioning their resonance upfield at δ=0 ppm\delta = 0\text{ ppm}δ=0 ppm.
The four carbon atoms in TMS are in different chemical environments, producing a set of four distinct peaks that allow for precise multi-point calibration of the 13C^{13}\text{C}13C chemical shift scale.
TMS is a highly polar, non-volatile liquid that mixes readily with deuterated water (D2O\text{D}_2\text{O}D2O), ensuring excellent sample homogeneity in aqueous NMR.
The protons in TMS are highly deshielded due to the electron-withdrawing nature of the central silicon atom, resulting in a single intense signal downfield of most organic signals.
28 exam-style questions on OCR A A Level Chemistry Spectroscopy. Each one has a worked solution and a mark scheme showing where the marks go.