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Electrophilic Addition to Alkynes: Halogenation

Electrophilic Addition to Alkynes: Halogenation

Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.

Formation of Complex Ions

Formation of Complex Ions

A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...

Polyprotic Acids

Polyprotic Acids

Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:

Hydrogen Bonds

Hydrogen Bonds

A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...

Hydrogen Bonds

Hydrogen Bonds

Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
Hydrogen Bonds Control the World!
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared.

Lewis Structures of Molecular Compounds and Polyatomic Ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:

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Related Experiment Video

Updated: May 17, 2026

A Study of the Complexation of Mercury(II) with Dicysteinyl Tetrapeptides by Electrospray Ionization Mass Spectrometry

A Study of the Complexation of Mercury(II) with Dicysteinyl Tetrapeptides by Electrospray Ionization Mass Spectrometry

Published on: January 8, 2016

Cationic complexes of hydrogen with helium.

Peter Bartl¹, Christian Leidlmair, Stephan Denifl

¹Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria.

Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry

|October 24, 2012

Summary

Helium nanodroplets doped with hydrogen reveal stable helium-hydrogen cluster ions. The study identifies particularly stable helium-hydrogen ion stoichiometries, with the H(2)(+) ion showing high helium retention efficiency.

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Last Updated: May 17, 2026

A Study of the Complexation of Mercury(II) with Dicysteinyl Tetrapeptides by Electrospray Ionization Mass Spectrometry

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Published on: January 8, 2016

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Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

Published on: May 15, 2015

Area of Science:

Physical Chemistry
Atomic and Molecular Physics
Condensed Matter Physics

Background:

Helium nanodroplets are a unique medium for studying weakly bound systems.
Understanding the interaction between helium and atomic/molecular ions is crucial for cluster science.

Purpose of the Study:

To investigate the formation and stability of helium-hydrogen cluster ions.
To identify particularly stable stoichiometries within these clusters.
To compare helium retention efficiency between different hydrogen ion species.

Main Methods:

High-resolution mass spectrometry of helium nanodroplets doped with hydrogen or deuterium.
Analysis of ion yields for various helium-hydrogen cluster ion stoichiometries (He(n)H(x)(+)).

Main Results:

Copious helium binding to H(+), H(2)(+), H(3)(+), and larger hydrogen cluster ions was observed.
All conceivable He(n)H(x)(+) stoichiometries below ≈120 u were identified.
Anomalies in ion yields indicated particularly stable cluster ions, including a pronounced anomaly for He(12)H(3)(+).
The H(2)(+) monomer ion demonstrated significantly higher helium retention efficiency compared to hydrogen cluster ions.

Conclusions:

The study provides comprehensive data on helium-hydrogen cluster ion formation and stability.
Specific stoichiometries, such as He(12)H(3)(+), represent particularly stable configurations.
The high helium affinity of the H(2)(+) ion is a key finding, contrasting with other dopant molecules.