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Chapter 19: Amines Back To Chapter

19.12: Mass Spectrometry of Amines

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Mass Spectrometry of Amines

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19.10: NMR Spectroscopy Of Amines

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19.13: Preparation of Amines: Alkylation of Ammonia and Amines

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In mass spectrometry, molecules are ionized and broken down into relatively stable, smaller species.

In a mass spectrometer, amines undergo fragmentation by breaking the bond between α and β carbons—also called α cleavage— producing an iminium ion and an alkyl radical.

The mass spectrum of an amine follows the nitrogen rule—a compound with an odd number of nitrogen atom generates a parent ion with an odd molecular weight and a fragment ion with an even molecular weight.

For example, butyl propyl amine has a parent ion peak at m/z 115, confirming the presence of odd number of nitrogen atoms in the molecule.

Since the molecule has two alkyl chains connected to N, α cleavage can occur via two modes.

α cleavage on the butyl side chain yields iminium ion with loss of propyl radical. The iminium fragment peak at m/z 72 is the base peak.

α cleavage on the propyl side chain yields an iminium ion with a peak observed at m/z 86, along with the loss of ethyl radical.

19.12: Mass Spectrometry of Amines

In mass spectroscopy, amines undergo fragmentation to give parent ions with odd molecule weights. This observed mass spectrum follows the nitrogen rule: a molecule with an odd number of nitrogen atoms produces a parent ion with an odd molecular weight. The remaining fragments have an even mass.

Amines undergo fragmentation through α cleavage, producing nitrogen-containing cations—iminium ions—and alkyl radicals. Mass spectra of aromatic and cyclic aliphatic amines exhibit strong molecular ion peaks, but acyclic aliphatic amines show weaker molecular ion peaks.

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Mass Spectrometry Amines Fragmentation Parent Ions Nitrogen Rule Mass Spectrum Nitrogen Atoms Molecular Weight Fragments Î±-cleavage Iminium Ions Alkyl Radicals Aromatic Amines Cyclic Aliphatic Amines Acyclic Aliphatic Amines

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