# A chemist uses high-resolution NMR spectroscopy to identify an unknown organic compound. The compound produces three distinct peaks in its ¹H NMR spectrum. Explain how a chemist uses ¹H NMR spectroscopy to determine the structure of an organic compound, including how the number of peaks, chemical shift values, and integration (relative peak areas) each contribute to identifying the compound.

> Edexcel A-Level Chemistry (9CH0) — 19.1 NMR and chromatography · Explain · 5 marks

> An unknown organic compound is analysed using ¹H NMR spectroscopy. The spectrum shows three peaks at chemical shift values of 1.2 ppm, 2.4 ppm, and 9.8 ppm, with relative peak areas in the ratio 6:2:1.

## Mark scheme (5 marks)

1. The number of peaks indicates the number of different chemical environments of hydrogen atoms (protons) in the molecule.
2. Chemical shift values indicate the type of chemical environment each set of protons is in, allowing identification of functional groups present.
3. Integration (relative peak areas) shows the ratio of the number of protons in each environment; a ratio of 6:2:1 indicates 6, 2, and 1 proton(s) respectively.
4. TMS (tetramethylsilane) is used as the reference standard, set at 0 ppm, against which all chemical shift values are measured.
5. By combining information from the number of peaks, chemical shift values, and integration, the chemist can deduce the full structure of the molecule; the data here is consistent with a molecule such as 3-methylbutanal (or similar aldehyde with a CH₃CH₂– and (CH₃)₂CH– type environment).

## Key terms

- [¹H NMR spectroscopy](https://www.gradenine.co.uk/glossary/h-nmr-spectroscopy)
- [chemical shift](https://www.gradenine.co.uk/glossary/chemical-shift)
- [integration](https://www.gradenine.co.uk/glossary/integration)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-chemist-uses-high-resolution-nmr-spectroscopy-7185f2bd) · Published by Druglandscape Ltd.