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Cambridge International AS & A Level Chemistry – Organic Chemistry

Topic 22
Analytical
Techniques

Topic 22 covers the analysis of infrared spectra to identify functional groups from the data section, and mass spectra: m/e values and isotopic abundances, the molecular ion peak and relative molecular mass, fragmentation, the [M+1]⁺ peak used to count carbon atoms, and the [M+2]⁺ peaks that show chlorine or bromine. The identification page combines both with the chemical tests met in Topics 15 to 17.

Exam Papers
Papers 1 & 2
9701 AS Level
Learning Outcomes
22.1 – 22.2
2 sections covered
Topic Parts
3 pages
Revision notes available
Exam Board
Cambridge
9701 (2025 onwards)

Revision Notes

Work through Topic 22 Analytical Techniques in a structured sequence.

m/z
Mass
Spectra
1
Available

Mass Spectra of Organic Compounds

Mass spectra of organic compounds: molecular ion, m/z, fragmentation patterns, common fragments, M+2 peaks for chlorine and bromine.

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Wavenumber / cm⁻¹
Infrared
Spectroscopy
2
Available

Infrared Spectroscopy

Infrared spectroscopy: bond vibrations, wavenumbers, characteristic absorptions of functional groups, broad O–H bands, the fingerprint region and identifying compounds.

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Evidence to structure
Identifying
Unknowns
3
Available

Identifying Unknown Compounds

Identifying unknown organic compounds: combining the molecular ion, fragmentation, infrared absorptions and chemical tests, with a worked example.

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Specification Coverage

Topic 22 Analytical Techniques – Cambridge International AS Level Chemistry

The following Cambridge learning outcomes state what candidates should be able to do. Wording is taken from the Cambridge International AS & A Level Chemistry (9701) syllabus.

22.1 Infrared spectroscopy

22.1.1
analyse an infrared spectrum of a simple molecule to identify functional groups (see the Data section for the functional groups required)

22.2 Mass spectrometry

22.2.1-a
analyse mass spectra in terms of m/e values (knowledge of the working of the mass spectrometer is not required)
22.2.1-b
analyse mass spectra in terms of isotopic abundances (knowledge of the working of the mass spectrometer is not required)
22.2.2-a
calculate the relative atomic mass of an element given the relative abundances of its isotopes
22.2.2-b
calculate the relative atomic mass of an element given its mass spectrum
22.2.3
deduce the molecular mass of an organic molecule from the molecular ion peak in a mass spectrum
22.2.4
suggest the identity of molecules formed by simple fragmentation in a given mass spectrum
22.2.5
deduce the number of carbon atoms, n, in a compound using the [M+1]⁺ peak and the formula n = (100 × abundance of [M+1]⁺ ion) / (1.1 × abundance of M+ ion)
22.2.6-a
deduce the presence of bromine atoms in a compound using the [M+2]⁺ peak
22.2.6-b
deduce the presence of chlorine atoms in a compound using the [M+2]⁺ peak