Name: alkyne mass spectra and key peaks
Uploaded: 2024-12-05T18:32:20.000Z
Duration: 53 s
Channel: JoVE

Alkine fragmentieren typischerweise und bilden das 3-Propinylkation oder Propargylkation, das resonanzstabilisiert ist.
Die Alkine können entweder terminal oder intern sein.
In terminalen Alkinen tritt das 3-Propinyl-Kationensignal bei einem Masse-Ladungs-Verhältnis von 39 auf. In internen Alkinen ist das 3-Propinylkation substituiert und tritt in einem höheren Masse-Ladungs-Verhältnis auf.
Eine weitere Art der Fragmentierung, die häufig beobachtet wird, ist der Verlust des Wasserstoffatoms aus dem terminalen Alkinkohlenstoff, der die Dreifachbindung trägt.
Endständige Alkine weisen also ein intensives Massensignal bei einem Masse-Ladungs-Verhältnis auf, das 1 μe niedriger ist als das Molekülion des Analytmoleküls. Dieser Gipfel wird als M-1-Gipfel bezeichnet.

massenspektrometrie: alkinfragmentierung

Mass Spectrometry: Alkyne Fragmentation

Die Fragmentierung von Alkinen erfolgt bevorzugt an der Kohlenstoff-Kohlenstoff-Bindung zwischen dem α- und β-Kohlenstoff der Alkinbindung und erzeugt ein 3-Propinylkation (oder Propargylkation). Bei terminalen Alkinen gibt es die einzige Fragmentierungsart, die das 3-Propinylkation ergibt. Das unsubstituierte 3-Propinylkation weist einen Peak bei einem Masse-zu-Ladung-Verhältnis von 39 auf. Bei internen Alkinen ist das 3-Propinylkation substituiert. Beispielsweise fragmentiert 2-Pentin in ein methyl-substituiertes 3-Propinylkation, das anschließend als Massensignal bei einem Masse-Ladungs-Verhältnis von 56 auftritt. Das 3-Propinylkation ist resonanzstabilisiert und das entsprechende Massensignal ist im Massenspektrum von Alkinen intensiv. Abbildung 1 zeigt die Fragmentierung von 1-Pentin in ein Ethylradikal und ein resonanzstabilisiertes 3-Propinylkation.

<img alt="Figure1" src="/files/ftp_upload/13045/13045-PT_Figure_1.svg" style="height: 115px;">

Abbildung 1: Fragmentierung des 1-Pentin-Molekülions zum 3-Propinylkation.

Ein weiterer Fragmentierungsweg, der bei terminalen Alkinen beobachtet wird, ist der Verlust von Wasserstoff vom terminalen sp-Kohlenstoff. Dies führt zu einem Massensignal mit einem Masse-zu-Ladung-Verhältnis von einer Einheit weniger als beim Molekülion. Dieser M–1-Peak ist sehr intensiv und wird zum Basispeak in den Massenspektren vieler Alkine, sodass er zur Identifizierung von Alkinen verwendet werden kann.

<img alt="Figure2" src="/files/ftp_upload/13045/13045-PT_Figure_2.svg" style="height: 275px;">

Abbildung 2: Das Massenspektrum von 1-Pentin.

Massenspektrometrie: Alkinfragmentierung

Die Fragmentierung von Alkinen erfolgt bevorzugt an der Kohlenstoff-Kohlenstoff-Bindung zwischen dem α und β Kohlenstoff der Alkinbindung, um eine ...

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Analytical Chemistry

Analytische Chemie

Unit 1

Einheit 1

Mass Spectrometry Fragmentation Methods

Fragmentierungsmethoden der Massenspektrometrie

KEY TERMS AND CONCEPTS

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alkyne mass spectra and key peaks

Alkyne mass spectra often show strong peaks from two main fragmentation paths. One path breaks the carbon-carbon bond between the alpha and beta carbons of the alkyne bond. This produces a 3-propynyl cation, also called a propargyl cation.

In terminal alkynes, this is the only fragmentation path that gives the 3-propynyl cation. The unsubstituted 3-propynyl cation appears at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne forms a methyl-substituted 3-propynyl cation, which gives a mass signal at m/z 56.

The 3-propynyl cation is resonance-stabilized. That stability makes its signal intense in the mass spectrum of alkynes. A related example is the fragmentation of 1-pentyne, which produces an ethyl radical and a resonance-stabilized 3-propynyl cation.

Terminal alkynes can also lose hydrogen from the terminal sp carbon. This gives a mass signal that is one unit less than the molecular ion. The M-1 peak is often very intense and can become the base peak in many alkyne mass spectra. Because of this, it can help identify alkynes, including 1-pentyne.

Alkyne Mass Spectra and Key Peaks

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mass spectrometry: alkyne fragmentation

Alkyne mass spectra often show strong peaks from two main fragmentation paths. One path breaks the carbon-carbon bond between the alpha and beta carbons of the alkyne bond. This produces a 3-propynyl cation, also called a propargyl cation. In terminal alkynes, this is the only fragmentation path that gives the 3-propynyl cation. The unsubstituted 3-propynyl cation appears at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne forms a...

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Learn how alkynes fragment in mass spectrometry, including the 3-propynyl cation, m/z 39 and 56 peaks, and the strong M-1 peak in terminal alkynes.

Alkyne Mass Spectra and Key Peaks | JoVE K12

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Alkyne Mass Spectra and Key Peaks

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