Unsaturated Hydrocarbons

What are Unsaturated Hydrocarbons?

Unsaturated hydrocarbons are organic compounds that are entirely made up of carbon and hydrogen atoms and consist of a double or a triple bond between two adjacent carbon atoms. The hydrocarbons having at least one double bond between two adjacent carbon atoms are called alkenes, whereas the hydrocarbons which contain a carbon-carbon triple bond are referred to as alkynes. The difference in the chemical formulae of saturated and unsaturated hydrocarbons is illustrated below.

Unsaturated Hydrocarbons

In the IUPAC nomenclature of unsaturated hydrocarbons, the position of the double or triple bond is either described by a number written before the name of the compound (as in 2,4 pentadiene) or by a number written before the suffix, ‘-ene’ or ‘-yne’ (as in pent-2-ene).

The physical properties of saturated hydrocarbons and unsaturated hydrocarbons are quite similar. These types of hydrocarbons (with the exception of aromatic hydrocarbons) are quite reactive and tend to undergo addition reactions with elemental halogens, hydrogen halides, alcohols, and many other compounds.

Types of Unsaturated Hydrocarbons

Unsaturated hydrocarbons, based on the types of bonds they contain, can be classified into alkenes, alkynes, and aromatic hydrocarbons. The different types of organic compounds that can be classified as unsaturated hydrocarbons are briefly discussed below.

  • The hydrocarbons that contain at least one double bond between two adjacent carbon atoms are called alkenes or olefins. The simplest alkene is ethylene (or ethene), given by the chemical formula C2H4.
  • Alkenes containing only one double bond and having no functional groups or substituents attached to them can be generalized to the chemical formula CnH2n.
  • Hydrocarbons containing a minimum of one triple bond between two carbon atoms that are positioned adjacent to each other are referred to as alkynes. The alkyne with the simplest structure is acetylene (systematic IUPAC name: ethyne) with the chemical formula C2H2.
  • The alkynes that have only one carbon-carbon triple bond and have no functional or substituent groups attached to them can be generalized to the chemical formula CnH2n-2
  • Cyclic hydrocarbons that contain at least one double or triple bond between two carbon atoms are also considered to be unsaturated hydrocarbons, one such example being cyclopentene (C5H8).
  • Although Aromatic Hydrocarbons (ring-shaped hydrocarbons that contain delocalized pi electrons) can be considered as unsaturated hydrocarbons, they are generally referred to as aromatic compounds because they are relatively stable and do not share similar properties with other such unsaturated compounds.

In order to check whether a given hydrocarbon is unsaturated, bromine water can be added to it. Should the bromine water become decolorized, the hydrocarbon in question is unsaturated. If a white precipitate is formed, the hydrocarbon sample is a phenol or aniline. It can be noted that benzene does not decolorize the bromine water.

Uses of Unsaturated Hydrocarbons

Some uses of compounds belonging to the unsaturated hydrocarbon category are listed below.

  • Many fruits can be artificially ripened with the help of alkenes.
  • Mustard gas, a poisonous gas used in chemical warfare, can be created with the help of alkenes.
  • Unsaturated hydrocarbons are extremely useful organic compounds in the manufacturing of plastics.
  • LDPE, which is a low-density variation of polyethylene, is used in the manufacturing of grocery bags
  • Polystyrene is used in making egg cartons, disposable cups, and other convenient products.
  • Industrial chemicals such as alcohols include the usage of alkenes in their manufacturing process.
  • Some unsaturated hydrocarbons are used as general anesthetics.
  • Many organic compounds of high industrial importance are manufactured with the help of alkynes.

Thus, the general properties, types, and uses of unsaturated hydrocarbons are briefly discussed in this article. For more information on unsaturated hydrocarbons and other types of hydrocarbons, such as aromatic hydrocarbons, register with BYJU’S and download the mobile application on your smartphone.

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