Interpreting the infrared spectrum of N-methylethanamine (ethylmethylamine)

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 N-methylethanamine (ethylmethylamine)

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

Interpretation of the infrared spectrum of N-methylethanamine (ethylmethylamine)

The most prominent infrared absorption lines of N-methylethanamine (ethylmethylamine).

Without the actual infrared spectrum of N-methyethanamine, all I can offer is what you might expect!

At wavenumbers ~3500 to 3300 cm^-1 is a broad band for N-H bond stretching vibrations, characteristic of amines like N-methyethanamine.

Primary amines have a highly polar bond (^δ-N-H^δ+) and the intermolecular forces are increased by permanent dipole - permanent dipole attractions including hydrogen bonding (N-H^δ+llll^δ-N-H) between the N-methylethanamine molecules.

The hydrogen bonding interferes with the N-H stretching vibrations producing a broad band peaking at around ~3400 cm^-1.

Around 3000 to 2800 cm^-1 are absorptions due to C-H stretching vibrations - they overlap with the N-H stretching vibrations of N-methylethanamine.

N-CH₃ vibrations occur at wavenumbers 2820 to 2760 cm^-1 and overlap with the C-H vibration absorptions quoted above.

There are also characteristic bands due to N-H vibrations at wavenumbers ~1650 to 1580 cm^-1, often sharp, so do not confuse with the C=O vibrations from carbonyl compounds.

Absorption due to C-N vibrations, characteristic of C-N bonds in aliphatic amines like N-methylethanamine occur at 1250 to 1020 cm^-1.

There are other N-H vibration absorptions at wavenumbers ~910 to 665 cm^-1,

The absence of other specific functional group bands will show that a particular functional group is absent from the N-methylethanamine (ethylmethylamine) molecular structure.