Home Chemistry Hydrocarbon


What is a Hydrocarbon?

In organic chemistry, hydrocarbon is the simplest organic compound formed by bonding hydrogen with carbon and is found in natural gas, coal, and petroleum oil. Therefore, hydrocarbons are the parent or simplest organic compounds containing only carbon and hydrogen atoms in their molecules. All other organic compounds are derived from hydrocarbons by the replacement of one or more hydrogen atoms with other atoms or groups of atoms.

Hydrocarbon definition, types, topics, and, facts about saturated and unsaturated hydrocarbons

Methane (CH4), ethane (C2H6), ethylene (C2H4), and acetylene (C2H2) are common examples of hydrocarbons that are used widely in our daily lives. Such types of organic compounds are used in our homes as a source of energy.

Saturated Hydrocarbons

The organic molecules in which all the carbon atoms are linked by only single covalent bonds are called saturated hydrocarbons (alkanes or paraffins). The general chemical formula of these compounds is CnH2n+2, where n = number of carbon atoms in one molecule of a hydrocarbon.

  • If there is only one carbon atom, the formula should be C1H(2×1+2) = CH4 (methane).
  • Similarly, if there are two carbon atoms in alkane, the formula should be C2H(2×2+2) = C2H6 (ethane).


Cycloalkanes are saturated hydrocarbons that contain closed rings comprised of carbon atoms only. These compounds are collectively called carbocyclic or homocyclic compounds.

Cycloalkanes are also alicyclic saturated hydrocarbons with general molecular formula CnH2(n+1−r), where n = number of carbon atoms and r = number of ring/rings in one cycloalkane molecule.

  • When the number of ring one, the general molecular formula = CnH2n. Therefore, the molecular formula of cyclopentane = C5H10 and cyclohexane = C6H12.
  • If the number of ring two, the general molecular formula = CnH2n−2.
  • When the number of rings is three, the general molecular formula = CnH2n−4.

The most important class of monocyclic cycloalkanes occurs in petroleum and terpenes. Generally, six-membered cycloalkanes are found in petroleum, and five-membered cycloalkanes are found in terpenes.

Many cyclic acids also occur in petroleum. These are the cyclopentane derivatives of naphthalic acids.

Unsaturated Hydrocarbons

The organic compounds which contain at least one double or triple bond along with single bonds are called unsaturated hydrocarbons. These are more reactive than saturated hydrocarbons. They generally undergo addition reactions.

Unsaturated hydrocarbons are further divided into the following two categories:

  1. Alkenes or Olefins
  2. Alkynes

Alkenes or Olefins

The unsaturated hydrons that have at least one double bond along with single bonds are called alkenes or olefins. A double bond in an alkene molecule is formed by the sharing of two pairs of electrons between the two carbon atoms.

The name olefin arose from the fact that ethylene is called olefiant gas or oil-forming gas because it formed oily liquids when treated with chlorine or bromine. The general molecular formula of alkenes is CnH2n. Therefore the molecular formula of ethene = C2H4, propene = C3H6, butene = C4H8, etc.

When the hydrocarbons contain two double bonds, they are called diolefins or alkadiene. The general molecular formula of these organic compounds is CnH2n−2. Similarly, when three double bonds are present, the compounds are named tri-olefins or alkatrienes with the general molecular formula CnH2n−4.

Monocyclic Cycloalkenes

Monocyclic cycloalkenes are also unsaturated hydrocarbons containing one ring of carbon atoms and one or more double bonds in the ring but they do not form an aromatic ring.

The general molecular formula of monocyclic cycloalkenes with only one double bond is CnH2(n−r). Therefore, the molecular formula of cyclopropene = C3H4, cyclobutene = C4H6, cyclopentene = C5H8, cyclohexene = C6H10, and cycloheptene = C7H12.


Alkynes are unsaturated hydrocarbons that have one or more triple bonds along with single bonds. A triple bond in an alkyne molecule is formed by the sharing of 3 pairs of electrons between two carbon atoms. The general molecular formula of alkynes is CnH2n−2.

  • If an alkynes have two carbon atoms, the formula is C2H(2×2−2) = C2H2 (ethyne).
  • If there are three carbon atoms in the alkyne, the formula should be = C3H(2×3−2) = C3H4 (propyne).
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