Introduction to Alkynes
Quantum mechanics helps us in a great deal to study the structure of different molecules found in nature. The concept of chemical bonding in combination with quantum mechanics has revealed numerous information about various organic and inorganic compounds that are essential for life. This article deals with the structure of a special class of organic compounds known as alkynes. Acetylene is the simplest member of the alkyne family. Alkynes are unsaturated hydrocarbons in which a carbon-carbon triple bond exists between the two carbon atoms.
What is a triple bond?
When three pairs of electrons are shared between two carbon atoms, a triple bond is formed between the two carbon atoms. The distinguishing features of alkynes from the other hydrocarbons are the triple bond which exists between the carbon atoms.
The triple bonded carbon atoms of acetylene are hybridized. Sigma bond between the atoms of carbon is obtained by a head-on overlapping of the two hybridized sp orbitals. The leftover orbitals of the carbon atoms overlap with each other along the internuclear axis in the 1s orbital of each hydrogen atom which results in the formation of one C-H sigma bond and 2 weaker pi bonds. These bonds are formed due to orbital overlapping. Each carbon atom uses only one of its three p-orbitals.
Hence, the two remaining p orbitals are occupied by a single electron. As it is same with the other carbon atom, this permits the pairing of electrons which results in the formation of 2 pi bonds. The carbon-carbon triple bond is made stronger by the presence of one sigma bond.
Acetylene is a linear molecule with carbon-carbon distance of 1.21Ao. The C-H distance in acetylene is 1.08 shorter than alkenes due to the fact that sp hybridized carbon has more s character than the sp2 hybridized carbon.
Uses of Alkynes
The most common form of alkynes Ethyne is used in preparing many other compounds. some of these uses are as follows:
- The most common use of Ethyne is for making organic compounds like ethanol, ethanoic acid, acrylic acid, etc.
- It is also used for making polymers and its beginning materials. For instance, vinyl chloride is used as the starting material for PVC and chloroprene is used for synthetic rubber neoprene.
- Ethyne is used for preparing many organic solvents.
- Alkynes are commonly used to artificially ripe fruits.
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