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

Les amines subissent un clivage ⍺ dans le spectromètre de masse pour produire un cation azoté stabilisé par résonance et un radical alkyle.
Il est intéressant de noter que pour les amines, le nombre d’atomes d’azote dans le composé affecte le poids moléculaire de l’ion moléculaire, également appelé règle de l’azote de la spectrométrie de masse.
Selon la règle, un composé organique neutre contenant un nombre impair d’atomes d’azote produira un ion moléculaire de poids moléculaire impair.
Par exemple, considérez le spectre de masse de la triéthylamine, qui a un atome d’azote.
Ici, l’ion moléculaire a un rapport masse/charge étrange de 101.
La fragmentation de l’ion moléculaire lors du clivage ⍺ libère un radical méthyle et génère un pic de base à un rapport masse/charge de 86.

spectrométrie de masse: fragmentation des amines

Mass Spectrometry: Amine Fragmentation

Les amines peuvent être identifiées à l'aide de la spectroscopie de masse en fonction de leurs schémas de fragmentation caractéristiques. Les ions moléculaires des amines subissent une fragmentation par clivage ⍺. Le clivage ⍺ des liaisons carbone-carbone dans les amines génère un radical alkyle et un cation contenant de l'azote stabilisé par résonance.

Dans les amines, le nombre d'atomes d'azote affecte la masse de l'ion moléculaire, qui est décrite par la règle de l'azote de la spectrométrie de masse. Cette règle stipule qu'un composé contenant un seul atome d'azote ou un nombre impair d'atomes d'azote produit un ion moléculaire de poids moléculaire impair, tandis qu'un composé sans atome d'azote ou avec un nombre pair d'atomes d'azote génère un ion moléculaire de poids moléculaire pair.

Par exemple, le spectre de masse de la 3-méthyl-1-butanamine, qui contient un atome d'azote, présente un ion moléculaire ayant un rapport masse/charge impair de 87. La fragmentation de cet ion moléculaire par clivage ⍺ produit un pic de base, qui présente un signal de masse à un rapport masse/charge de 30, correspondant à la perte du radical 2-méthylpropyle.

De même, la fragmentation de la triéthylamine par clivage ⍺ génère un cation à un rapport masse/charge de 86. Le pic de l'ion moléculaire présente un rapport masse/charge impair de 101, comme indiqué ci-dessous.

<img alt="Figure1" src="/files/ftp_upload/13048/13048_PT_Figure_1.svg" style="height: 105px;">

Spectrométrie de masse: fragmentation des amines

Les amines peuvent être identifiées à l’aide de la spectroscopie de masse en fonction de leurs modèles de fragmentation caractéristiques. Les ions moléculaires des amines subissent une fragmentation ...

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Mass Spectrometry Fragmentation Methods

Méthodes de fragmentation en spectrométrie de masse

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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

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Amines in Mass Spectra: Nitrogen Rule

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