Interpreting the infrared spectrum of ethyl methanoate (ethyl formate)

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 ethyl methanoate

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

Interpretation of the infrared spectrum of ethyl methanoate

The most prominent infrared absorption lines of ethyl methanoate

C-H stretching vibration absorptions occur in the wavenumber region 2975 to 2860 cm^-1.

Not very important, common to most organic molecules.

For saturated aliphatic esters, C=O stretching vibration absorptions occur in the wavenumber region 1750 to 1735 cm^-1.

This is a very characteristic absorption for any molecule e.g. an ester, with a carbonyl group.

For ethanoate esters, C-O stretching vibration absorptions occur in the wavenumber region 1200 to 1180 cm^-1.

The absence of other specific functional group bands will show that a particular functional group is absent from the ethyl methanoate molecular structure e.g. no hydroxyl group vibration at ~3500 to 3200 cm^-1., obviously not expected for an ester like methyl ethanoate, but expected for a carboxylic acid like the isomeric propanoic acid.