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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.

Halogenation of Alkenes

Halogenation of Alkenes

Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.

Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions

Diazonium Group Substitution with Halogens and Cyanide: Sandmeyer and Schiemann Reactions

Arenediazonium substitution reactions occur when the diazonium group is substituted by various functional groups such as halides, hydroxyl, nitrile, etc. For instance, arenediazonium salts react with copper(I) salts of chloride, bromide, or cyanide to form corresponding aryl chlorides, bromides, and nitriles. These reactions are named Sandmeyer reactions. Although the mechanism of this reaction is complicated, as illustrated in Figure 1, they are believed to progress via an aryl copper...

Radical Halogenation: Thermodynamics

Radical Halogenation: Thermodynamics

The thermodynamic favorability of a reaction is determined by the change in Gibbs free energy (ΔG). ΔG has two components- enthalpy (ΔH) and entropy (ΔS). The entropy component is negligible for alkane halogenation because the number of reactants and product molecules are equal. In this case, the ΔG is governed only by the enthalpy component. The most crucial factor that determines ΔH is the strength of the bonds. ΔH can be determined by comparing the energy...

Radical Halogenation: Stereochemistry

Radical Halogenation: Stereochemistry

Stereochemistry is the study of the different spatial arrangements of atoms in a given molecule. The stereochemistry of radical halogenations can be understood from three different situations:
Halogenation to form a new chiral center:

Reactions at the Benzylic Position: Halogenation

Reactions at the Benzylic Position: Halogenation

Benzylic halogenation takes place under conditions that favor radical reactions such as heat, light, or a free radical initiator like peroxide.

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In Vitro Method to Control Concentrations of Halogenated Gases in Cultured Alveolar Epithelial Cells

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Anomalous Halogen-Halogen Interaction Assists Radial Chromophoric Assembly.

M A Niyas¹, Remya Ramakrishnan¹, Vishnu Vijay¹

¹School of Chemistry , Indian Institute of Science Education and Research Thiruvananthapuram , Vithura, Thiruvananthapuram , Kerala , India 695551.

Journal of the American Chemical Society

|February 12, 2019

Summary

Researchers discovered a stable hexabromine synthon (Br6) that forms a symmetric radial assembly. This finding advances understanding of halogen bonding, revealing its stabilizing nature and potential in supramolecular chemistry.

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Area of Science:

Supramolecular Chemistry
Crystal Engineering
Chemical Physics

Background:

Designing efficient supramolecular architectures requires understanding noncovalent interactions.
Halogen bonding is a key noncovalent interaction, forming halogen-halogen (X2) and trihalogen synthons.

Purpose of the Study:

To report the first observation of a symmetric radial assembly of chromophores.
To investigate the nature, role, and potential of noncovalent halogen bonding using a novel hexabromine synthon (Br6).

Main Methods:

Experimental observation of a symmetric radial assembly with R3̅c space group.
Analysis of Type-I X2 interactions within the Br6 synthon.
Investigation of intermolecular through-space charge transfer interactions.

Main Results:

First observation of a stable hexabromine (Br6) synthon forming a 3-fold symmetric radial assembly.
Type-I X2 interactions in the Br6 synthon exhibit stabilizing properties, contrary to previous proposals.
The assembly is strengthened by charge transfer interactions, forming a lattice reminiscent of light-harvesting systems.

Conclusions:

The Br6 synthon represents a new stable interacting unit, expanding the scope of halogen bonding applications.
Halogen bonding, particularly Type-I X2 interactions, can be stabilizing due to the exchange-correlation component.
The observed radial assembly has implications for designing artificial light-harvesting systems and other functional supramolecular materials.