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Advanced Organic Chemistry: Infrared spectrum of propylamine

Interpreting the infrared spectrum of propylamine (1-aminopropane)

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 propylamine

infrared spectrum of propylamine wavenumbers cm-1 functional group detection fingerprint pattern identification of propylamine doc brown's advanced organic chemistry revision notes 

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

propylamine, (1-aminopropane), C3H9N, (c) doc b , (c) doc b , (c) doc b

Interpretation of the infrared spectrum of propylamine

The most prominent infrared absorption lines of propylamine

At ~wavenumbers 3500 to 3300 cm-1 are 'twin peaks' for N-H bond stretching vibrations, these twin bands are characteristic of primary amines.

Primary 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 propylamine molecules (diagram below).

The hydrogen bonding interferes with the N-H stretching vibrations often producing a broad absorption band.

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

There are also characteristic bands due to N-H vibrations at wavenumbers ~1650 to 1580 cm-1.

Absorption due to C-N vibrations, characteristic of C-N bonds in aliphatic amines occur at 1220 to 1020 cm-1.

Around 3000 to 2800 are absorptions due to C-H stretching vibrations and tend to overlap with the N-H stretching vibration absorptions.

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


Key words & phrases: image and diagram of the infrared spectrum of propylamine, complete infrared absorption spectrum of propylamine, comparative spectra of propylamine, prominent peaks/troughs for identifying functional groups in the infrared spectrum of propylamine, important wavenumber values in cm-1 for peaks/troughs in the infrared spectrum of propylamine, revision of infrared spectroscopy of propylamine, fingerprint region analysis of propylamine, how to identify propylamine from its infrared spectrum, identifying organic compounds like propylamine from their infrared spectrum, how to analyse the absorption bands in the infrared spectrum of propylamine detection of functional groups in the propylamine molecule other names 1-aminopropane n-propylamine 1-propanamine 1-propylamine


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