Interpreting the infrared spectrum of 2-bromopropane

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 2-bromopropane

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Spectra obtained from a liquid film of 2-bromopropane. The right-hand part of the of the infrared spectrum of 2-bromopropane, wavenumbers ~1500 to 400 cm^-1 is considered the fingerprint region for the identification of 2-bromopropane and most organic compounds. It is due to a unique set of complex overlapping vibrations of the atoms of the molecule of 2-bromopropane.

Interpretation of the infrared spectrum of 2-bromopropane

The most prominent infrared absorption lines of 2-bromopropane

Several moderately strong absorption bands at wavenumbers 2975 to 2845 cm^-1 for C-H stretching vibrations - collectively give the impression of strong absorption in the infrared spectrum of 2-bromopropane.

Several strong absorption bands from C-H deformation vibrations at wavenumbers 1470 to 1370 cm^-1.

C-C-C skeletal vibrations from the C(CH₃)2 grouping give absorptions bands with wavenumbers 1175 to 1140 and 840 to 790 cm^-1.

Several strong absorption bands ~550 cm^-1 due to C-Br stretching vibrations of 2-bromopropane.

The absence of other specific functional group bands will show that a particular functional group is absent from the 2-bromopropane molecular structure.