(420) AQA 3.4 Alkenes REVISION

Introduction to Alkenes

• Overview of the alkenes topic in chemistry.

• Presented by Chris Harris from AllerTutors.com.

• Designed to ensure students understand the relevant information and specifications related to alkenes.

• PowerPoint materials available for purchase in the video description for further revision.

What are Alkenes?

• Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C).

• General formula for alkenes: CnH2n.

• Examples include ethene (C2H4) and propene (C3H6).

Characteristics of Alkenes

• Unsaturation: Alkenes are unsaturated due to the presence of double bonds, unlike alkanes, which are saturated.

• Reactivity: Alkenes are more reactive than alkanes due to the double bond.

  • They undergo addition reactions where reactants add to the carbon atoms involved in the double bond.

Reactions of Alkenes

• Addition Reactions:

  • Hydrogenation: Addition of hydrogen (H2) to form alkanes.

  • Halogenation: Reaction with halogens (e.g., Br2) to form dihaloalkanes.

  • Hydrohalogenation: Addition of hydrogen halides (e.g., HCl) to form haloalkanes.

  • Hydration: Addition of water (H2O), typically in the presence of an acid, to form alcohols.

Isomerism in Alkenes

• Geometric Isomerism: Arises due to the restricted rotation around the double bond, leading to cis-trans isomers.

• Structural Isomerism: Different connectivity of the carbon atoms in the molecule, leading to variations such as chain isomers.

Importance of Alkenes in Industry

• Alkenes are used as starting materials for the synthesis of plastics, alcohols, and other chemicals.

• Ethene is a key raw material in the production of polyethylene, one of the most widely used plastics.

• They play a significant role in organic synthesis and the petrochemical industry.