NEET Chemistry Notes Hydrocarbons – Alkynes
Alkynes
Alkynes
Alkynes are also unsaturated hydrocarbons. They contain at least one triple bond between two carbon atoms. Their general formula is CnH2n _ 2
Physical Properties of Alkynes
- All alkynes are odourless, however acetylene has garlic smell due to the impurity of phosphine.
- The melting and boiling points of alkynes are slightly higher than those of the corresponding alkenes and alkanes.
Chemical Properties of Alkynes
The alkynes exhibit the chemical properties as listed below:
- Electrophilic Additidn Reactions
The reaction, called hydration of alkynes, is used commercially for the preparation of aldehydes and ketones.
Nucleophilic Addition Reactions
Reactions Showing Acidic Character of Alkynes
Terminal alkynes have acidic H because C—H bond has ionic character due to resonance
Oxidation
Oxidation by acidic KMn04 (hot)
Wilkinson’s catalyst reduces alkenes and alkynes without affecting common functional groups such as C = O,—CN and —N02 etc.
Polymerisation
Linear polymerisation Ethyne undergoes linear polymerisation under suitable conditions to produce polyacetylene or polyethyne,
