Interpreting the infrared spectrum of propanamide (propionamide)

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 propanamide

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

propanamide (propionamide), C₃H₇NO, , ,

Interpretation of the infrared spectrum of propanamide

The most prominent infrared absorption lines of propanamide

Characteristic N-H stretching vibration absorption bands at wavenumbers 3500 to 3200 cm^-1.

A very prominent C=O stretching vibration absorption at wavenumbers 1690 to 1650 cm^-1, characteristic of all molecules with a carbonyl group.

But, this is complicated by combined N-H deformation and C-N stretching vibrations absorbing at 1650 to 1590 cm^-1.

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