Page 2: Isomerism and Physical Properties of Alkenes and Alkynes
This page delves deeper into the isomerism of alkenes and alkynes, and discusses their physical properties.
Structural isomerism is further explored, including chain isomerism and position isomerism. The page introduces geometric isomerism cis−transisomerism specific to alkenes, which occurs due to the restricted rotation around the carbon-carbon double bond.
Example: Cis-but-2-ene and trans-but-2-ene demonstrate geometric isomerism in alkenes.
Physical properties of alkenes and alkynes are discussed:
- State of matter: Gases C1−C4, liquids C5−C15, and solids C16+
- Volatility: Decreases with increasing carbon chain length
- Boiling point, melting point, and density: Generally increase with carbon chain length exceptforalkynemeltingpoints
The page also introduces dienes, compounds with two double bonds in their molecules.
Vocabulary: Dienes are hydrocarbons containing two carbon-carbon double bonds.
Methods for synthesizing alkenes are briefly mentioned:
- Dehydration of alcohols using Al₂O₃ as a catalyst at high temperatures
- Dehydrohalogenation of haloalkanes using alcoholic solutions of strong bases
Highlight: The synthesis of alkenes often involves elimination reactions, where smaller molecules are removed to form the carbon-carbon double bond.