Alkenes

Alkenes

Definition and Basic Understanding

  • Alkenes are a part of Organic compounds, falling under the category of unsaturated hydrocarbons.
  • They contain at least one double bond between the carbon atoms in their molecules. The general formula that defines alkenes is CnH2n.

Characteristics of Alkenes

  • Alkenes are described as unsaturated hydrocarbons, this is due to the presence of the double bond. This allows the alkenes to react easily with other molecules.
  • Compared to alkanes that are saturated hydrocarbons, alkenes are typically more reactive. This is because the double bond presents an area of high electron density, making it likely for electrophiles to attack.

Functional and Structural Similarities

  • The double bond in alkenes is the functional group. This functional group allows alkenes to undergo addition reactions.
  • Alkenes can also engage in polymerization reactions forming long chain polymers.

Naming Alkenes

  • The naming of alkenes follows the IUPAC nomenclature similar to other homologous series. The smallest alkene, with two carbon atoms and a double bond, is named as Ethene (C2H4).
  • Alkenes are named based on the longest carbon chain containing the double bond. The position of this bond is indicated by a number before the name if it is not obvious.

Examples of Alkenes

  • Common examples of alkenes include Ethene (C2H4), Propene (C3H6), and Butene (C4H8).

Physical Properties of Alkenes

  • Alkenes are generally colourless gases or liquids. As their molecular weight increases, they can become waxy solids.
  • Ethene, Propene and Butene are all gases at room temperature. They are also less dense than water.

Chemical Properties of Alkenes

  • The characteristic reaction of alkenes is addition reaction due to the presence of the double bond. They can react with halogen gases (X2) to form dihalogeno compounds.
  • They can also react with hydrogen in the presence of a catalyst to form alkanes.

Isomerism in Alkenes

  • Alkenes exhibit geometric isomerism. This occurs due to the restricted rotation around the double bond. The atoms or groups attached to the carbon atoms of the double bond can be arranged differently, giving rise to different compounds with the same molecular formula but different structures.