ALKENES

By German Fernandez, 30 May, 2024

Nomenclature of Alkenes
The IUPAC names alkenes by changing the -ane ending of alkanes to -ene. The longest chain containing the double bond is chosen as the main chain and is numbered to give the double bond the lowest possible locator.

Alkenes exhibit cis/trans isomerism. For tri- and tetrasubstituted alkenes, the Z/E notation is used.

Double Bond Structure
Alkenes are planar with sp2 hybridized carbons. The double bond consists of a sigma bond formed by the overlap of sp2 hybrids and a pi bond formed by the overlap of p orbitals perpendicular to the molecular plane.

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JSmol model of lysergic acid

Double Bond Stability
Double bonds are stabilized by hyperconjugation, making an alkene more stable the more substituents are attached to the sp2 carbons.

Synthesis of Alkenes
Alkenes are obtained through elimination reactions from haloalkanes and dehydration of alcohols.

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JSmol model of quinine

Alkene Reactions
Alkenes add a variety of reagents to the double bond. They react with halogen acids, water in acidic medium, MCPBA, etc.

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