4.2.4
Analytical
Techniques
Section 4.2.4 covers infrared spectroscopy: bond vibrations, absorption by atmospheric gases and the link to global warming, identifying alcohols, aldehydes, ketones and carboxylic acids from their absorptions, monitoring air pollution and breathalysers; mass spectrometry: the molecular ion peak and fragmentation; and the deduction of structures from elemental analysis, mass spectra and infrared spectra together.
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
OCR A Level Chemistry A · 4.2.4 Analytical techniques
The whole section on one A4 page: the molecular ion, elemental analysis, fragmentation, infrared absorption, reading IR spectra, and PAG 4 and PAG 7, with worked examples.
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4.2.4
- b i
absorption of infrared radiation by atmospheric gases containing C=O, O–H and C–H bonds (e.g. CO2, H2O and CH4)
Revise - b ii
the suspected link between absorption of infrared radiation by atmospheric gases and global warming
Revise - c (i)
use of an infrared spectrum of an organic compound to identify an alcohol from an absorption peak of the O–H bond
Revise - c (ii)
use of an infrared spectrum of an organic compound to identify an aldehyde or ketone from an absorption peak of the C=O bond
Revise - c (iii)
use of an infrared spectrum of an organic compound to identify a carboxylic acid from an absorption peak of the C=O bond and a broad absorption peak of the O–H bond
Revise - d i
interpretations of an infrared spectrum of familiar or unfamiliar substances using supplied data
Revise - d ii
predictions of an infrared spectrum of familiar or unfamiliar substances using supplied data
Revise - e i
use of infrared spectroscopy to monitor gases causing air pollution (e.g. CO and NO from car emissions)
Revise - f ii
use of the molecular ion peak in a mass spectrum of an organic compound to determine molecular mass
Revise - h (i)
deduction of the structures of organic compounds from different analytical data including elemental analysis (see also 2.1.3 c)
Revise - h (ii)
deduction of the structures of organic compounds from different analytical data including mass spectra
Revise - h (iii)
deduction of the structures of organic compounds from different analytical data including IR spectra
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