Name: amines in mass spectra: nitrogen rule
Uploaded: 2024-12-05T18:32:20.000Z
Duration: 55 s
Channel: JoVE

Amine werden im Massenspektrometer einer ⍺-Spaltung unterzogen, um ein resonanzstabilisiertes stickstoffhaltiges Kation und einen Alkylrest zu erhalten.
Interessanterweise beeinflusst bei Aminen die Anzahl der Stickstoffatome in der Verbindung das Molekulargewicht des Molekülions, das in der Massenspektrometrie auch als Stickstoffregel bezeichnet wird.
Gemäß der Regel erzeugt eine neutrale organische Verbindung, die eine ungerade Anzahl von Stickstoffatomen enthält, ein Molekülion mit einem ungeraden Molekulargewicht.
Betrachten Sie zum Beispiel das Massenspektrum von Triethylamin, das ein Stickstoffatom hat.
Hier hat das Molekülion ein ungerades Masse-Ladungs-Verhältnis von 101.
Die Fragmentierung des Molekülions bei der ⍺-Spaltung setzt ein Methylradikal frei und erzeugt einen Basenpeak bei einem Masse-Ladungs-Verhältnis von 86.

massenspektrometrie: aminfragmentierung

Mass Spectrometry: Amine Fragmentation

Amine können mithilfe der Massenspektroskopie anhand ihrer charakteristischen Fragmentierungsmuster identifiziert werden. Die Molekülionen von Aminen werden durch ⍺-Spaltung fragmentiert. Die ⍺-Spaltung der Kohlenstoff-Kohlenstoff-Bindungen in Aminen erzeugt ein Alkylradikal und ein resonanzstabilisiertes stickstoffhaltiges Kation.

Bei Aminen beeinflusst die Anzahl der Stickstoffatome die Masse des Molekülions, was durch die Stickstoffregel der Massenspektrometrie beschrieben wird. Diese Regel besagt, dass eine Verbindung mit einem einzigen oder einer ungeraden Anzahl von Stickstoffatomen ein Molekülion mit einem ungeraden Molekulargewicht erzeugt, während eine Verbindung mit keinem oder einer geraden Anzahl von Stickstoffatomen ein Molekülion mit einem geraden Molekulargewicht erzeugt.

Beispielsweise zeigt das Massenspektrum von 3-Methyl-1-butanamin, das ein Stickstoffatom enthält, ein Molekülion mit einem ungeraden Masse-zu-Ladung-Verhältnis von 87. Die Fragmentierung dieses Molekülions durch ⍺-Spaltung erzeugt einen Basispeak, der ein Massensignal bei einem Masse-zu-Ladung-Verhältnis von 30 aufweist, was dem Verlust des 2-Methylpropylradikals entspricht.

In ähnlicher Weise erzeugt die Fragmentierung von Triethylamin durch ⍺-Spaltung ein Kation bei einem Masse-zu-Ladung-Verhältnis von 86. Der Molekülionenpeak zeigt ein ungerades Masse-zu-Ladung-Verhältnis von 101, wie unten gezeigt.

<img alt="Figure1" src="/files/ftp_upload/13048/13048_PT_Figure_1.svg" style="height: 105px;">

Massenspektrometrie: Aminfragmentierung

Amine können mittels Massenspektroskopie anhand ihrer charakteristischen Fragmentierungsmuster identifiziert werden. Die Molekülionen der Amine werden fragmentiert ...

Education

Lehre

JoVE Core

Analytical Chemistry

Analytische Chemie

Unit 1

Einheit 1

Mass Spectrometry Fragmentation Methods

Fragmentierungsmethoden der Massenspektrometrie

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

amines in mass spectra: nitrogen rule

Amines can be identified in mass spectrometry by their fragmentation patterns and by the nitrogen rule. The molecular ions of amines often break apart through β-cleavage, which cuts a carbon-carbon bond next to the nitrogen. This process forms an alkyl radical and a resonance-stabilized nitrogen-containing cation.

The nitrogen rule helps predict the mass of the molecular ion. A compound with one nitrogen atom, or any odd number of nitrogen atoms, gives a molecular ion with an odd molecular weight. A compound with no nitrogen atoms, or an even number of nitrogen atoms, gives a molecular ion with an even molecular weight.

The mass spectrum of 3-methyl-1-butanamine shows this pattern clearly. Because it contains one nitrogen atom, its molecular ion appears at m/z 87, which is odd. Fragmentation by β-cleavage gives a base peak at m/z 30, after loss of the 2-methyl propyl radical.

Triethylamine shows a similar fragmentation pattern. Its molecular ion appears at m/z 101, and β-cleavage produces a cation at m/z 86. These peaks help identify amines by linking molecular ion mass with their characteristic breakdown products.

Amines in Mass Spectra: Nitrogen Rule

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key terms and concepts

Learn how amines fragment in mass spectrometry, how β-cleavage works, and how the nitrogen rule helps predict odd or even molecular ion masses.

Amines in Mass Spectra: Nitrogen Rule | JoVE K12

analytical chemistry

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Amines in Mass Spectra: Nitrogen Rule

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