CHEMISTRY OF ALKYNES

Introduction

Alkynes are hydrocarbons that contain carbon–carbon triple bonds. Alkynes are also called acetylenes because they are derivatives of acetylene, the simplest alkyne. The carbon atoms of acetylene are connected by σ + π + π triple bond. Both carbon atoms are sp-hybridized, and each is bonded to a hydrogen by σ bond.

The chemistry of the carbon–carbon triple bond is similar to that of the double bond. In this chapter, we see that alkynes undergo most of the same reactions as alkenes, especially the additions and the oxidations.

 

Physical properties of Alkynes

1. Being compounds of low polarity, the alkynes have physical properties that are essentially the same as those of the alkanes and alkenes.

2. They are insoluble in water but quite soluble in the usual organic solvents of low polarity: ligroin, ether, benzene, carbon tetrachloride.

3. They are less dense than water.

4.Their boiling points show the usual increase with increasing carbon number, and the usual effects of chain-branching; they are very nearly the same as the boiling points of alkanes or alkenes with the same carbon skeletons.

 

Chemical Properties of Alkynes

 

 

 

 

 

Preparation of Alkynes

A carbon-carbon triple bond is formed in the same way as a double bond: elimination of atoms or groups from two adjacent carbons. The groups eliminated and and the reagents used are demonstrated below: