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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.

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...

Preparation of Alkynes: Dehydrohalogenation

Preparation of Alkynes: Dehydrohalogenation

Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.

Qualitative Analysis

Qualitative Analysis

For solutions containing mixtures of different cations, the identity of each cation can be determined by qualitative analysis. This technique involves a series of selective precipitations with different chemical reagents, each reaction producing a characteristic precipitate for a specific group of cations. Metal ions within a group are further separated by varying the pH, heating the mixture to redissolve a precipitate, or adding other reagents to form complex ions.
For instance, group IV...

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...

Relative Stabilities of Alkenes

Relative Stabilities of Alkenes

The relative stability of alkenes can be determined by comparing their heats of hydrogenation. The lower heat of hydrogenation indicates the more stable alkene. The three main factors determining the relative stability of alkenes are i) the number of substituents attached to the double-bond carbon atoms, ii) hyperconjugation, and iii) the stereochemistry of the double bond.

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Updated: May 1, 2026

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

1-Alkenylcalcium iodide: synthesis and stability.

Mathias Köhler¹, Helmar Görls, Jens Langer

¹Friedrich Schiller University Jena, Institute of Inorganic and Analytical Chemistry, Humboldtstrasse 8, 07743 Jena (Germany), Fax: (+49) 3641-948132.

Chemistry (Weinheim an Der Bergstrasse, Germany)

|March 29, 2014

Summary

Researchers developed a new heavy calcium-based Grignard reagent from 1,2-dihydro-4-iodonaphthalene. This 1-alkenylcalcium complex, while less stable than aromatic analogs, expands the utility of calcium reagents in synthesis.

Keywords:

Grignard reaction alkenylcalcium complexes calcium direct synthesis reduction reactions

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Synthesis and Purification of Iodoaziridines Involving Quantitative Selection of the Optimal Stationary Phase for Chromatography

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Published on: May 16, 2014

Area of Science:

Organometallic Chemistry
Calcium Chemistry

Background:

Heavy calcium-based Grignard reagents are valuable synthetic tools.
Expanding the scope of these reagents is crucial for organic synthesis.

Purpose of the Study:

To synthesize and characterize a novel 1-alkenylcalcium complex.
To investigate the stability of this new calcium derivative.

Main Methods:

Reduction of 1,2-dihydro-4-iodonaphthalene with calcium in tetrahydrofuran (THF).
X-ray structure determination and Nuclear Magnetic Resonance (NMR) spectroscopy for characterization.

Main Results:

Successfully synthesized tetrakis(thf) (1,2-dihydronaphth-4-yl)calcium iodide.
Confirmed the structure as a 1-alkenylcalcium complex.
Observed significantly reduced stability compared to aromatic naphthylcalcium iodide.

Conclusions:

The new 1-alkenylcalcium complex broadens the scope of calcium-based Grignard reagents.
The reduced stability highlights the unique reactivity of alkenyl calcium species.