Interpreting the infrared spectrum of ethyl ethanoate (ethyl acetate)

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 ethanoate

email doc brown

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

Ethyl ethanoate C₄H₈O₂  , , ,  

Interpretation of the infrared spectrum of ethyl ethanoate

The most prominent infrared absorption lines of ethyl ethanoate

C-H stretching vibrations occur at wavenumbers 2975 to 2845 cm^-1.

The most characteristic band is at wavenumbers ~1750 to 1735 cm^-1, for the carbonyl C=O bond stretching vibrations.

For ethanoate esters the C-O stretching vibration absorptions occur at wavenumbers 1250 to 1230 cm^-1.

The absence of other specific functional group bands will show that particular functional group is absent from the ethyl ethanoate molecular structure e.g. ester infrared spectra are easily distinguished from isomeric carboxylic acids by the absence of the broad O-H band at 3300 to 2500 cm^-1.