Interpreting the infrared spectrum of methanol CH₃OH  (re-edit)

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 methanol

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

Interpretation of the infrared spectrum of methanol

The most prominent infrared absorption lines of methanol

The very characteristic strong absorption band for the O-H stretching vibrations at wavenumbers 3400 to 3200 cm^-1.

This absorption band is broadened by the intermolecular hydrogen bonding interactions between the hydroxyl groups of adjacent methanol molecules.

Hydrogen bonding (llll) between methanol molecules  CH₃-O–H^δ+llll^δ–:O-CH₃

The absorption bands ~2900 cm^-1 arise from C-H bond stretching vibrations - common to most organic molecules.

There are several strong absorptions bands at wavenumbers 1075 to 1000 cm^-1 and 1350 to 1260 cm^-1 from the stretching vibrations of the C-O bond.

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

In this case there is a strong broad characteristic absorption of a molecule with a hydroxyl group exhibiting intermolecular hydrogen bonding e.g. aliphatic alcohols.