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

Las aminas se someten a una escisión ⍺ en el espectrómetro de masas para producir un catión que contiene nitrógeno estabilizado por resonancia y un radical alquilo.
Curiosamente para las aminas, el número de átomos de nitrógeno en el compuesto afecta el peso molecular del ion molecular, también llamado la regla del nitrógeno de la espectrometría de masas.
Según la regla, un compuesto orgánico neutro que contenga un número impar de átomos de nitrógeno producirá un ion molecular con un peso molecular impar.
Por ejemplo, considere el espectro de masas de la trietilamina, que tiene un átomo de nitrógeno.
Aquí, el ion molecular tiene una relación masa a carga impar de 101.
La fragmentación del ion molecular en la escisión libera un radical metilo y genera un pico de base con una relación masa-carga de 86.

espectrometría de masas: fragmentación de aminas

Mass Spectrometry: Amine Fragmentation

Las aminas se pueden identificar mediante espectroscopia de masas en función de sus patrones característicos de fragmentación. Los iones moleculares de las aminas sufren fragmentación mediante escisión ⍺. La escisión ⍺ de los enlaces carbono-carbono en las aminas genera un radical alquilo y un catión que contiene nitrógeno estabilizado por resonancia.
En las aminas, la cantidad de átomos de nitrógeno afecta la masa del ion molecular, que se describe mediante la regla del nitrógeno de la espectrometría de masas. Esta regla establece que un compuesto que contiene un solo átomo de nitrógeno o un número impar de átomos de nitrógeno produce un ion molecular con un peso molecular impar, mientras que un compuesto sin átomos de nitrógeno o con un número par de átomos de nitrógeno genera un ion molecular con un peso molecular par.
Por ejemplo, el espectro de masas de la 3-metil-1-butanamina, que contiene un átomo de nitrógeno, muestra un ion molecular que tiene una relación masa-carga impar de 87. La fragmentación de este ion molecular a través de la escisión ⍺ produce un pico de base, que presenta una señal de masa en una relación masa-carga de 30, que corresponde con la pérdida del radical 2-metilpropilo.
De manera similar, la fragmentación de la trietilamina a través de la escisión ⍺ genera un catión en una relación masa-carga de 86. El pico del ion molecular muestra una relación masa-carga impar de 101, como se muestra a continuación.
<img alt="Figure1" src="/files/ftp_upload/13048/13048_PT_Figure_1.svg" style="height: 105px;">

Espectrometría de masas: fragmentación de aminas

Las aminas se pueden identificar mediante espectroscopia de masas en función de sus patrones de fragmentación característicos. Los iones moleculares de las aminas sufren fragmentación ...

Education

Educación

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidad 1

Mass Spectrometry Fragmentation Methods

Métodos de fragmentación en espectrometría de masas

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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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