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Alkyl Halides

Alkyl Halides

Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...

Complexation Equilibria: Factors Influencing Stability of Complexes

Complexation Equilibria: Factors Influencing Stability of Complexes

In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...

Halogens

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. Astatine is a highly unstable radioactive element, so currently, most of its properties are unknown due to its short half-life. Tennessine is a synthetic element also predicted to be in this group.

Ionic Bonding and Electron Transfer

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence shell, and an anion (a negative ion) forms when a neutral atom gains one or more electrons in its valence shell. Compounds composed of ions are called ionic compounds (or salts), and their constituent ions are held together by ionic bonds: electrostatic forces of attraction between oppositely charged cations and anions.

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.

ortho–para-Directing Deactivators: Halogens

ortho–para-Directing Deactivators: Halogens

Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...

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Related Experiment Video

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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Published on: March 24, 2018

Stabilizing Otherwise Unstable Anions with Halogen Bonding.

Xinxing Zhang^1,2, Gaoxiang Liu¹, Sandra Ciborowski¹

¹Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA.

Angewandte Chemie (International Ed. in English)

|July 1, 2017

Summary

Halogen bonding (XB) can stabilize unstable anions, like the pyrazine anion, by forming complexes with bromobenzene. This interaction creates a positive electron affinity (EA) for the neutral complexes, a novel finding in chemical bonding research.

Keywords:

anions density functional theory halogen bonding hydrogen bonding photoelectron spectroscopy

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Published on: April 2, 2015

Area of Science:

Chemical Physics
Supramolecular Chemistry
Computational Chemistry

Background:

Hydrogen bonding (HB) is known to stabilize anions, but the anion-stabilizing ability of halogen bonding (XB) is less understood.
Pyrazine anion is unstable in isolation due to its neutral form having a negative electron affinity (EA).

Purpose of the Study:

To investigate the halogen bond-stabilization of the pyrazine anion.
To determine if halogen bonding can induce a positive electron affinity in otherwise unstable anions.

Main Methods:

Anion photoelectron spectroscopy was used to study the electronic properties of the complexes.
Density functional theory (DFT) calculations were employed to analyze the electronic structure and interactions.
Charge distribution and electrostatic potential analyses were performed.

Main Results:

Halogen bonding between bromobenzene and pyrazine significantly stabilized the pyrazine anion in complexes like Pz(BrPh)₁^- and Pz(BrPh)₂^-.
The formation of these complexes resulted in a positive electron affinity for the neutral complexes, indicating stabilization.
Charge distribution analysis showed dilution of the negative charge on the pyrazine anion due to XB.

Conclusions:

Halogen bonding is a viable mechanism for stabilizing unstable anions.
The study demonstrates the emergence of positive electron affinity in neutral complexes stabilized by halogen bonding.
Low temperatures during supersonic expansion are crucial for the formation of these halogen-bonded complexes.