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

Les alcynes se fragmentent généralement pour former le cation 3-propynyle ou cation propargyle, qui est stabilisé par résonance.
Les alcynes peuvent être terminaux ou internes.
Dans les alcynes terminaux, le signal du cation 3-propynyle apparaît à un rapport masse/charge de 39. Dans les alcynes internes, le cation 3-propynyle est substitué et apparaît à un rapport masse/charge plus élevé.
Un autre type de fragmentation fréquemment observé est la perte de l’atome d’hydrogène de l’alcyne terminal du carbone porteur de la triple liaison.
Ainsi, les alcynes terminaux présentent un signal de masse intense à un rapport masse/charge de 1 u inférieur à l’ion moléculaire de la molécule d’analyte. Ce pic est désigné par le pic M-1.

spectrométrie de masse: fragmentation des alcynes

Mass Spectrometry: Alkyne Fragmentation

La fragmentation des alcynes se produit préférentiellement au niveau de la liaison carbone-carbone entre les carbones α et β de la liaison alcyne pour générer un cation 3-propynyle (ou cation propargyle). Dans les alcynes terminaux, il existe le seul type de fragmentation qui donne le cation 3-propynyle. Le cation 3-propynyle non substitué présente un pic à un rapport masse/charge de 39. Dans les alcynes internes, le cation 3-propynyle est substitué. Par exemple, le 2-pentyne se fragmente en cation 3-propynyle substitué par méthyle, qui apparaît ensuite comme un signal de masse au rapport masse/charge de 56. Le cation 3-propynyle est stabilisé par résonance et le signal de masse correspondant est intense dans le spectre de masse des alcynes. La figure 1 montre la fragmentation du 1-pentyne en un radical éthyle et un cation 3-propynyle stabilisé par résonance.

<img alt="Figure1" src="/files/ftp_upload/13045/13045-PT_Figure_1.svg" style="height: 115px;">

Figure 1: Fragmentation de l'ion moléculaire 1-pentyne pour produire le cation 3-propynyle.

Une autre voie de fragmentation observée dans les alcynes terminaux est la perte d'hydrogène du carbone sp terminal. Cela se traduit par un signal de masse avec un rapport masse/charge d'une unité inférieure à celui de l'ion moléculaire. Ce pic M–1 est très intense et devient le pic de base dans les spectres de masse de nombreux alcynes, il peut donc être utilisé pour identifier les alcynes.

<img alt="Figure2" src="/files/ftp_upload/13045/13045-PT_Figure_2.svg" style="height: 275px;">

Figure 2: Le spectre de masse du 1-pentyne.

Spectrométrie de masse: fragmentation des alcynes

La fragmentation des alcynes se produit préférentiellement au niveau de la liaison carbone-carbone entre le carbone α et β carbone de la liaison alcyne pour générer un ...

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Analytical Chemistry

Chimie analytique

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Mass Spectrometry Fragmentation Methods

Méthodes de fragmentation en spectrométrie de masse

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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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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