Interpreting the infrared spectrum of cyclopentane

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 cyclopentane

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

Interpretation of the infrared spectrum of cyclopentane

The most prominent infrared absorption lines of cyclopentane

Most of these are due to the vibrations of the C-H bonds e.g. stretching and bending deformations at ~2900 cm^-1 and ~1460 cm^-1.

There is no characteristic absorption band for a functional group, as cycloalkanes don't have one.

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