Question:

The cylindrical shape of an alkyne is due to

Updated On: Aug 8, 2024
  • three sigma C-C bonds
  • three $π$C-C bonds
  • two sigma C-C and one $π$ C-C bonds
  • one sigma C-C and two $π$ C-C bonds
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The Correct Option is D

Solution and Explanation

The correct answer is D:one sigma \(C-C\) and two \(C-C \) bonds
In alkynes \(C \equiv C\) is present, in such bond one sigma and two \(π\)-bonds are present. Sigma bond is formed by sp-hybrid orbitals whereas \(π\)-bonds are formed by unhybridised orbitals. Hence, it shows cylindrical shape.
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Concepts Used:

Alkynes

In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon-carbon triple bond. Alkynes are an organic molecule that contains triple bonds between the carbon atoms. Its general formula is CnH2n-2. They are also known as acetylenes. In this article, we will deal with the structure of alkynes.

Isomerism in Alkynes:

Alkynes show three types of isomerism

  1. Chain isomerism - Due to the different arrangement of carbon atoms in the chain that is straight chain or branched.
  2. Position isomerism - Due to the difference in the location of the triple bond.
  3. Functional isomerism - Isomeric with alkadienes both being represented by the general formula CnH2n-1. 

Properties of Alkynes:

Physical Properties:

  • Non-polar, unsaturated hydrocarbons.
  • Highly soluble in organic and non-polar solvents and slightly soluble in polar solvents.
  • High boiling point, in comparison to other hydrocarbons.
  • Release a high amount of energy due to the repulsion of electrons in a reaction.
  • More acidic than alkanes and alkenes due to SP hybridization.

Chemical Properties:

  • Hydrogenation - Alkynes undergoes two types of hydrogenation reactions. Complete hydrogenation (in presence of Pd-C/ H2) and partial hydrogenation (in presence of Linder’s catalyst/H2).
  • Act as a strong nucleophile by converting into acetylide. 
  • React with BH3 and undergo hydroboration reactions to form aldehydes and ketones.
  • Undergo halogenation reactions in the presence of different halogenating agents by different mechanisms and forms haloalkanes.