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

Os alcinos normalmente se fragmentam para formar o cátion 3-propinil ou cátion propargil, que é estabilizado por ressonância.
Os alcinos podem ser terminais ou internos.
Nos alcinos terminais, o sinal do cátion 3-propinil aparece em uma relação massa-carga de 39. Nos alcinos internos, o cátion 3-propinil é substituído e aparece em uma relação massa-carga mais alta.
Outro tipo de fragmentação freqüentemente observado é a perda do átomo de hidrogênio do carbono alcino terminal que contém a ligação tripla.
Assim, os alcinos terminais exibem um sinal de massa intenso em uma relação massa-carga de 1 u menor que o íon molecular da molécula do analito. Este pico é denotado como o pico M-1.

espectrometria de massa: fragmentação de alcino

Mass Spectrometry: Alkyne Fragmentation

A fragmentação de alcinos ocorre preferencialmente na ligação carbono-carbono entre os carbonos α e β da ligação alcino para gerar um cátion 3-propinil (ou cátion propargil). Em alcinos terminais, há o único tipo de fragmentação que produz o cátion 3-propinil. O cátion 3-propinil não substituído exibe um pico em uma razão massa-carga de 39. Em alcinos internos, o cátion 3-propinil é substituído. Por exemplo, o 2-pentino se fragmenta em um cátion 3-propinil substituído por metil, que subsequentemente se apresenta como um sinal de massa na razão massa-carga de 56. O cátion 3-propinil é estabilizado por ressonância, e o sinal de massa correspondente é intenso no espectro de massa de alcinos. A Figura 1 mostra a fragmentação do 1-pentino em um radical etil e um cátion 3-propinil estabilizado por ressonância.

<img alt="Figure1" src="/files/ftp_upload/13045/13045-PT_Figure_1.svg" style="text-align: center; height: 115px;">

Figura 1: Fragmentação do íon molecular 1-pentino para produzir o cátion 3-propinil.

Outra via de fragmentação observada em alcinos terminais é a perda de hidrogênio do carbono sp terminal. Isso resulta em um sinal de massa com uma razão massa-carga de uma unidade a menos que o íon molecular. Esse pico M–1 é muito intenso e se torna o pico base nos espectros de massa de muitos alcinos, então pode ser usado para identificar alcinos.

<img alt="Figure2" src="/files/ftp_upload/13045/13045-PT_Figure_2.svg" style="text-align: center; height: 275px;">

Figura 2: O espectro de massa do 1-pentino.

Espectrometria de Massa: Fragmentação de Alcino

A fragmentação de alcinos ocorre preferencialmente na ligação carbono-carbono entre o α e β carbono da ligação alcino para gerar um ...

Education

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidade 1

Mass Spectrometry Fragmentation Methods

Métodos de Fragmentação em Espectrometria de Massas

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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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key terms and concepts

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

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Alkyne Mass Spectra and Key Peaks

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