Overview of Alkenes

  • Alkenes are a category of hydrocarbons that contain at least one carbon-carbon double bond.
  • These double bonds make alkenes unsaturated hydrocarbons.
  • The general formula for alkenes is CnH2n where ‘n’ is the number of carbon atoms.

Properties of Alkenes

  • The double bonds in alkenes give them greater reactivity than their alkane counterparts.
  • They are non-polar compounds and hence insoluble in water but soluble in organic solvents.
  • Like alkanes, as the length of the carbon chain increases, so does the boiling point of alkenes.

Nomenclature of Alkenes

  • The names of alkenes, similar to those of alkanes, start with a prefix denoting the number of carbon atoms (‘meth-’ for 1, ‘eth-’ for 2, ‘prop-’ for 3, and so forth).
  • This prefix is followed by the suffix ‘-ene’ to denote the presence of a carbon-carbon double bond.
  • If more than one double bond exists, the suffix changes to denote the number (‘-diene’ for two, ‘-triene’ for three, and so forth).

Isomerism in Alkenes

  • More structural isomerism potential exists in alkenes than alkanes due to the presence of double bonds.
  • They can exhibit both chain isomerism and position isomerism.
  • Alkenes with more than one double bond can display geometric isomerism.

Reactions of Alkenes

  • Alkenes can partake in addition reactions due to the presence of double bonds.
  • A common example of this is the reaction with bromine water, which decolourises in the presence of an alkene.
  • They can also undergo hydrogenation (addition of hydrogen in the presence of a catalyst) to become alkanes.
  • Alkenes also undergo combustion, burning in oxygen to produce carbon dioxide and water. However, incomplete combustion can produce carbon (soot) or carbon monoxide.