Understanding Alkynes: Properties, Preparation, Reactions, and Applications

alkynes

hydrocarbons with one triple bond are called ____________

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They have the general formula CnH2n-2 and are also known as acetylenes. Alkynes are unsaturated compounds, which means that they have the potential to undergo addition reactions to form new compounds.

Properties:
– Alkynes are non-polar molecules due to the absence of any polar functional group such as -OH, -COOH, etc.
– They have high boiling points compared to alkanes because of their triple bond, leading to a harder and stronger intermolecular force.

Preparation:
1. From Calcium carbide: Alkynes can be prepared from the reaction of calcium carbide and water. Calcium carbide reacts with water to form acetylene and calcium hydroxide. This process is referred to as the ethyne generating system.
2. Dehydrohalogenation: Elimination reactions of vicinal dihalides leads to the formation of alkynes.
3. By reduction of alkynes: Alkynes can be reduced to alkanes by a catalytic hydrogenation reaction.

Reactions:
1. Addition reactions: Alkynes can undergo addition reactions where molecules add to the triple bond. An example of an addition reaction is the reaction of hydrogen with ethyne to form ethene.
2. Hydration: Alkynes can undergo hydration in the presence of concentrated sulfuric acid and water to form ketones or aldehydes.
3. Hydrohalogenation: Alkynes can undergo hydrohalogenation where a hydrogen halide adds across the triple bond to form a halogenated alkene.
4. Ozonolysis: Alkynes can undergo ozonolysis in the presence of ozone to form carbonyl compounds and other functional groups.

Uses:
1. Alkynes are used in the production of polymers such as synthetic rubber.
2. They are used as starting materials in organic synthesis.
3. Alkynes are used in welding and metal cutting. The high temperature generated when acetylene combusts with oxygen produces a hot and concentrated flame that can be used in welding.
4. They are used as building blocks in the synthesis of pharmaceuticals and agrochemicals.

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