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.
Revision Notes
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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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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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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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Analysis Summary Map
Cambridge International AS & A Level Chemistry · Topic 22 Analytical techniques
The whole topic on one A4 page: the molecular ion, the M+1 and M+2 peaks, fragmentation, infrared absorption, reading IR spectra and qualitative analysis, with worked examples.
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22.1.1
- 22.1.1
analyse an infrared spectrum of a simple molecule to identify functional groups (see the Data section for the functional groups required)
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22.2.1
22.2.2
- a
calculate the relative atomic mass of an element given the relative abundances of its isotopes
- b
calculate the relative atomic mass of an element given its mass spectrum
22.2.3
- 22.2.3
deduce the molecular mass of an organic molecule from the molecular ion peak in a mass spectrum
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22.2.4
- 22.2.4
suggest the identity of molecules formed by simple fragmentation in a given mass spectrum
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22.2.5
- 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)
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22.2.6
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