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Mass Spectrometry: Long-Chain Alkane Fragmentation01:18

Mass Spectrometry: Long-Chain Alkane Fragmentation

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The molecular ions of linear alkanes prefer to fragment at the carbon-carbon bond away from the end of the chain since the cleavage of an inner bond creates a stable carbocation and a stable radical. Consequently, the mass signals of linear alkanes feature intense peaks in the middle of the mass-to-charge ratio plot with weaker peaks on either end. The fragmentation of each carbon-carbon bond with the release of a methyl group in each splitting leads to prominent peaks in the mass spectra...
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Mass Spectrometry: Cycloalkane Fragmentation01:05

Mass Spectrometry: Cycloalkane Fragmentation

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In mass spectrometry, cycloalkanes exhibit distinct fragmentation patterns due to the inherent stability of their molecular ions compared to linear or branched alkanes. The ring structure of cycloalkanes provides additional stability to the molecular ions, often resulting in prominent ion peaks in the mass spectrum.
For example, cyclohexane molecular ions have a mass-to-charge ratio (m/z) of 84, which tends to produce a stronger signal than linear alkanes like hexane. This stability comes from...
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Mass Spectrometry: Branched Alkane Fragmentation01:29

Mass Spectrometry: Branched Alkane Fragmentation

1.8K
This lesson delves into the mass spectrometry of branched alkane fragmentation. Branched alkanes possess secondary or tertiary carbon atoms, which generate relatively stable carbocations if the cleavage occurs at the branching point. The high stability of carbocations drives the instant fragmentation of branched alkanes. Accordingly, the branched alkane's molecular ion peak is very weak or invisible in the mass spectra, especially in comparison to a linear alkane.
1.8K
Inductive Effects on Chemical Shift: Overview01:27

Inductive Effects on Chemical Shift: Overview

2.3K
The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...
2.3K
Mass Spectrometry: Molecular Fragmentation Overview01:20

Mass Spectrometry: Molecular Fragmentation Overview

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The ionization of a molecule into a molecular ion inside the mass spectrometer causes instability in the molecule's structure due to the loss of an electron. This eventually leads to the fragmentation or breaking of some bonds in the molecule. The fragmentation occurs predominantly at specific bonds to yield relatively stable fragments.
One type of fragmentation pattern is the cleavage of a single bond in the molecular ion. The cleavage leads to a radical and a cation. The cleavage can occur at...
5.9K
Mass Spectrometry: Alkyl Halide Fragmentation01:22

Mass Spectrometry: Alkyl Halide Fragmentation

1.6K
Chlorine isotopes exist as 35Cl and 37Cl in a 3:1 ratio, while bromine isotopes exist as 79Br and 81Br in a 1:1 ratio. The mass spectrum of alkyl halides typically produces two distinct molecular ion peaks, the molecular ion peak, [M], and the molecular ion plus two, [M + 2] peak. The relative heights of these two peaks are proportional to the isotopic abundance ratios of the halide. For example, 2‐chloropropane and 1‐bromopropane display two peaks with relative peak heights in a 3:1 and...
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Updated: Feb 23, 2026

In Situ SIMS and IR Spectroscopy of Well-defined Surfaces Prepared by Soft Landing of Mass-selected Ions
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Selective C-H Bond Cleavage in Methane by Small Gold Clusters.

Sandra M Lang1, Thorsten M Bernhardt1, Valeriy Chernyy2

  • 1Institute of Surface Chemistry and Catalysis, University of Ulm, Albert-Einstein-Allee 47, 89069, Ulm, Germany.

Angewandte Chemie (International Ed. in English)
|September 5, 2017
PubMed
Summary

Researchers developed gold cluster catalysts that selectively break methane

Keywords:
C−H bond activationab initio calculationscluster compoundsgoldvibrational spectroscopy

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Area of Science:

  • Catalysis research
  • Materials science
  • Computational chemistry

Background:

  • Methane is a primary component of natural gas, mainly used for energy.
  • Converting methane into valuable chemicals requires selective C-H bond cleavage.
  • Developing catalysts for this conversion is a significant challenge.

Purpose of the Study:

  • To investigate the interaction of methane with small gold cluster cations.
  • To understand the mechanism of selective C-H bond dissociation in methane.
  • To identify key factors enabling selective methane conversion.

Main Methods:

  • Infrared spectroscopy to probe molecular interactions.
  • First-principles calculations to model reaction mechanisms.
  • Analysis of gold cluster cation interactions with methane.

Main Results:

  • Small gold cluster cations selectively dissociate C-H bonds in methane.
  • Formation of hydrido methyl complexes (H-Aux+ -CH3) observed.
  • Selective bond cleavage attributed to gold's electronic and relativistic properties.

Conclusions:

  • Gold cluster cations offer a novel pathway for selective methane functionalization.
  • The catalyst's selectivity arises from a balance of electronic and relativistic effects.
  • This understanding can guide the rational design of future catalysts.