Interpreting the infrared spectrum of chlorobenzene

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced A level organic chemistry students US K12 grade 11 grade 12 organic chemistry courses involving molecular spectroscopy analysing infrared spectra of chlorobenzene

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Spectra obtained from a liquid film of chlorobenzene. The right-hand part of the of the infrared spectrum of chlorobenzene, wavenumbers ~1500 to 400 cm^-1 is considered the fingerprint region for the identification of chlorobenzene and most organic compounds. It is due to a unique set of complex overlapping vibrations of the atoms of the molecule of chlorobenzene.

Interpretation of the infrared spectrum of chlorobenzene

The most prominent infrared absorption lines of chlorobenzene

C-H stretching vibrations of the benzene ring, wavenumbers 3080 to 3030 cm^-1.

Several bands of strong absorptions with peaks at wavenumbers ~1500 and 1600 cm-1 from C=C stretching vibrations of the benzene ring.

Between wavenumbers 880 and 550 cm^-1 are several overlapping absorption bands from C-H and C-Cl vibrations.

The absence of other specific functional group bands will show that particular functional group is absent from the chlorobenzene molecular structure.