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Related Concept Videos

Acidity of 1-Alkynes02:42

Acidity of 1-Alkynes


The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
Structure and Physical Properties of Alkynes02:37

Structure and Physical Properties of Alkynes

Introduction:
In nature, compounds containing both carbon and hydrogen are known as "hydrocarbons". Aliphatic hydrocarbons are compounds whose molecules contain saturated single bonds (i.e., alkanes) or unsaturated double or triple bonds. Alkenes contain carbon–carbon double bonds and have a structural formula CnH2n. Unsaturated hydrocarbons containing carbon–carbon triple bonds are called "alkynes" and are structurally represented by the formula CnH2n-2.
The simplest alkyne is ethyne, or...
Chemical Ionization (CI) Mass Spectrometry01:21

Chemical Ionization (CI) Mass Spectrometry

The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the...
Electrophilic Aromatic Substitution: Friedel–Crafts Acylation of Benzene01:11

Electrophilic Aromatic Substitution: Friedel–Crafts Acylation of Benzene

The Friedel–Crafts acylation reactions involve the addition of an acyl group to an aromatic ring. These reactions proceed via electrophilic aromatic substitution by employing an acyl chloride and a Lewis acid catalyst such as aluminum chloride to form aryl ketone.
Mass Spectrometry: Cycloalkane Fragmentation01:05

Mass Spectrometry: Cycloalkane Fragmentation

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...
Nomenclature of Alkynes02:39

Nomenclature of Alkynes

Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes:

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Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F&#8722;
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Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−

Published on: July 27, 2018

Electron ionization of acetylene.

Simon J King1, Stephen D Price

  • 1Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.

The Journal of Chemical Physics
|November 13, 2007
PubMed
Summary

This study measured fragment ion yields from acetylene (C2H2) electron ionization. New data quantify contributions from multiple ionization events and reveal dissociation pathways for acetylene dications.

Area of Science:

  • Physical Chemistry
  • Atomic and Molecular Physics
  • Mass Spectrometry

Background:

  • Electron ionization of molecules produces fragment ions, crucial for understanding molecular structure and dynamics.
  • Acetylene (C2H2) fragmentation is complex, with multiple pathways and ionization states.
  • Previous studies on C2H2 ionization cross-sections show discrepancies.

Purpose of the Study:

  • To measure relative partial ionization cross sections for fragment ions from C2H2.
  • To quantify the contributions of single, double, and triple ionization to fragment ion yields.
  • To investigate the dissociation dynamics of the acetylene dication (C2H2+2).

Main Methods:

  • Time-of-flight mass spectrometry combined with a 2D ion-ion coincidence technique.

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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

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  • Measurement of relative partial ionization cross sections for various fragment ions (H+, H+2, C2+, etc.) as a function of electron energy (30-200 eV).
  • Derivation of branching ratios and kinetic energy release for C2H2+2 dissociation.

    • Main Results:

    • Excellent agreement with some previous absolute cross-section data, with discrepancies attributed to energetic ion loss in other studies.
    • Quantified contributions of multiple ionization: double ionization increases from 2% at 50 eV to over 10% at 100 eV.
    • Derived branching ratios for acetylene dication dissociation, indicating predominant dissociation via the triplet potential energy surface.

    Conclusions:

    • The study provides reliable relative partial ionization cross sections for C2H2.
    • New insights into the contributions of multiple ionization pathways and dication dissociation dynamics were obtained.
    • The findings support theoretical calculations regarding acetylene dication dissociation mechanisms.