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

Aminy ulegają ⍺-rozszczepieniu w spektrometrze masowym, aby uzyskać stabilizowany rezonansem kation zawierający azot i rodnik alkilowy.
Co ciekawe w przypadku amin, liczba atomów azotu w związku wpływa na masę cząsteczkową jonu cząsteczkowego, zwaną również regułą azotu w spektrometrii mas.
Zgodnie z regułą, obojętny związek organiczny zawierający nieparzystą liczbę atomów azotu wytworzy jon cząsteczkowy o nieparzystej masie cząsteczkowej.
Weźmy na przykład pod uwagę widmo masowe trietyloaminy, która ma jeden atom azotu.
Tutaj jon molekularny ma nieparzysty stosunek masy do ładunku wynoszący 101.
Fragmentacja jonu molekularnego po rozszczepieniu ⍺ uwalnia rodnik metylowy i generuje pik zasady przy stosunku masy do ładunku wynoszącym 86.

spektrometria masowa: fragmentacja aminy

Mass Spectrometry: Amine Fragmentation

Aminy można zidentyfikować za pomocą spektroskopii masowej na podstawie ich charakterystycznych wzorów fragmentacji. Jony cząsteczkowe amin ulegają fragmentacji poprzez rozszczepienie ⍺. Rozszczepienie wiązań węgiel-węgiel w aminach generuje rodnik alkilowy i kation zawierający azot stabilizowany rezonansowo.

W aminach liczba atomów azotu wpływa na masę jonu cząsteczkowego, co jest opisane przez regułę azotową spektrometrii masowej. Reguła ta stanowi, że związek zawierający pojedynczą lub nieparzystą liczbę atomów azotu wytwarza jon cząsteczkowy o nieparzystej masie cząsteczkowej, podczas gdy związek bez lub z parzystą liczbą atomów azotu generuje jon cząsteczkowy o parzystej masie cząsteczkowej.

Na przykład, widmo masowe 3-metylo-1-butanoaminy, która zawiera jeden atom azotu, pokazuje jon cząsteczkowy o nieparzystym stosunku masy do ładunku wynoszącym 87. Fragmentacja tego jonu cząsteczkowego poprzez rozszczepienie ⍺ wytwarza pik bazowy, który charakteryzuje się sygnałem masowym przy stosunku masy do ładunku wynoszącym 30, co odpowiada utracie rodnika 2-metylopropylowego.

Podobnie fragmentacja trietyloaminy poprzez rozszczepienie ⍺ generuje kation o stosunku masy do ładunku wynoszącym 86. Pik jonu cząsteczkowego wykazuje nieparzysty stosunek masy do ładunku wynoszący 101, jak pokazano poniżej.

<img alt="Figure1" src="/files/ftp_upload/13048/13048_PT_Figure_1.svg" style="text-align: center; height: 105px;">

Spektrometria masowa: Fragmentacja aminy

Aminy można zidentyfikować za pomocą spektroskopii mas na podstawie ich charakterystycznych wzorców fragmentacji. Jony molekularne amin ulegają fragmentacji ...

Education

JoVE Core

Analytical Chemistry

Chemia analityczna

Unit 1

Jednostka 1

Mass Spectrometry Fragmentation Methods

Metody fragmentacji w spektrometrii mas

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

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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