Advanced Organic Chemistry: Infrared spectrum of dimethylamine (CH3)2NH

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Interpreting and explaining the infrared spectrum of dimethylamine (N-methylmethanamine)

[Author © Dr Phil Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectrometry - analysing the infrared spectra of dimethylamine [spectra page updated April 3rd 2026 *]

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Introductory note on the infrared spectrum of dimethylamine

Students and teachers please note my explanation of the infrared spectrum of dimethylamine is designed for advanced, but pre-university, chemistry courses.

Based in the infrared spectrum diagram for dimethylamine, only some of the most prominent peaks for particular bond vibrations are discussed, particularly if dimethylamine has a functional group with a particular characteristic wavenumber peak.

The infrared spectrum of dimethylamine is unique and the whole, or selected wavenumbers, can be used to fingerprint its identity, sometimes analysing a mixture containing dimethylamine or following its change of concentration in a reaction.

infrared spectrum of dimethylamine C2H7N CH3NHCH3 wavenumbers cm-1 functional group detection fingerprint pattern identification of N-methylmethanamine doc brown's advanced organic chemistry revision notes 

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

Dimethylamine, N-methylmethanamine, C2H7N, (c) doc b , (c) doc b , (c) doc b

The classification, structure and naming of organic nitrogen compounds

Interpretation of the infrared spectrum of dimethylamine

The most prominent infrared absorption lines of dimethylamine

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

Secondary aliphatic amines have a highly polar bond (δ-N-Hδ+) and the intermolecular forces are increased by permanent dipole - permanent dipole attractions including hydrogen bonding (N-Hδ+llllδ-N-H) between the dimethylamine molecules (diagram below).

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

hydrogen bonding in aliphatic amines stronger intermolecular force bonds bonding higher boiling points compared to alkanes with no hydrogen bonding

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

There are also characteristic bands due to N-H deformation vibrations at wavenumbers ~1650 to 1550 cm-1 (for secondary amines), often fairly sharp, so do not confuse with the C=O vibrations from carbonyl compounds, which tend to be quite sharp.

Absorption due to C-N stretching vibrations, characteristic of C-N bonds in aliphatic amines like dimethylamine 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 dimethylamine molecular structure.

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