NMR Spectroscopy

Describe the process of NMR (7 steps)

1. Sample is placed in magnetic field

2. Atoms in molecule with an odd mass number either align with or against the magnetic field

3. Radio waves are passed through the sample

4. The combination of magnetic field and radio frequency radiation causes the nuclei to absorb energy and flip between 2 nuclear states

5. This is called resonance

6. Nuclei in different chemical environments require different amounts of energy to flip between states

7. The energy required to cause resonance can be detected and processed to give an NMR spectrum

Why can’t the solvent contain hydrogens in proton NMR

The signal from the hydrogen in the solvent would obscure the signals from the sample

What are the 2 solvents that can be used in NMR spectroscopy?

• CDCl₃

• CCl₄

What is used as the reference standard in NMR spectroscopy?

Tetramethylsilane (TMS)

What is the formula of TMS?

Si(CH₃)₄

What are the 3 key properties of TMS?

• Volatile (can be removed easily by evaporation)

• Unreactive

• Non-toxic