A-Level Chemistry AQA Notes

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Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR gives information about the position of 13C or 1H atoms in a molecule
Nuclei in different chemical environments in the sample molecule will resonate at different frequencies, allowing an NMR spectrum to be produced and interpreted.
Tetramethylsilane (TMS) is used as a standard to measure an NMR spectrum peak against. The 4 methyl groups are in the same chemical environment and produce an intense signal

A chemical shift is the scale used in NMR spectroscopy which relates to the difference in frequency between a chemical environment and TMS. It depends on the molecular environment.
The number of peaks in 13C NMR represents the number of carbon environments in a molecule
Each peak in a 1H NMR spectrum has an integration trace. This shows the relative number of 1H in each 1H environment
High resolution 1H also shows spin-spin coupling. This is useful because spin-spin coupling causes splitting patterns which give information about neighbouring hydrogen atoms. The splitting patterns are determined by the N+1 rule
The N+1 Rule- If there are n hydrogen atoms attached to carbon atoms adjacent to a 1H environment, then the peak representing that environment will be split into n+1 peaks

Common solvent used in NMR is CCl4. ie deuterated solvents.
In deuterated solvents, any H atoms are replaced with deuterium. They do not affect the spectra

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