Why is deuterated solvent used in NMR analysis?

Deuterated solvents are used in NMR analysis to prevent interference from the solvent's hydrogen atoms.

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the molecular structure of a compound. It works by applying an external magnetic field, which causes certain nuclei to resonate at characteristic frequencies. The resulting spectrum can be analysed to reveal details about the structure of the molecule.

However, most organic compounds are dissolved in a solvent for NMR analysis, and if this solvent contains hydrogen atoms, it can interfere with the spectrum. This is because the hydrogen atoms in the solvent will also resonate in the magnetic field, producing their own signals that can overlap with those of the compound being analysed. This makes it difficult to distinguish the signals from the compound and the solvent, and can lead to inaccurate results.

To overcome this problem, deuterated solvents are used. Deuterium is an isotope of hydrogen, with an extra neutron in its nucleus. This gives it different magnetic properties to regular hydrogen, so it resonates at a different frequency in the NMR machine. This means that the signals from the deuterium atoms in the solvent do not interfere with those from the hydrogen atoms in the compound being analysed.

Furthermore, deuterated solvents often contain a small amount of tetramethylsilane (TMS), which is used as a reference standard in NMR spectroscopy. TMS has a simple, well-defined spectrum, and by comparing the signals from the compound to those from the TMS, it is possible to accurately determine the structure of the compound.

In summary, deuterated solvents are essential for NMR analysis because they prevent interference from the solvent's hydrogen atoms, allowing the structure of the compound to be accurately determined.