Hydrocarbon

Hydrocarbon Types

Hydrocarbon in organic chemistry is the simplest list of organic compounds formed by bonding hydrogen with carbon and is classified as aliphatic and aromatic saturated and unsaturated molecules. Therefore, types of cyclic and noncyclic organic compounds that contain only carbon and hydrogen atoms in their molecules are called hydrocarbons. Hydrocarbons are found in natural gas, coal, and petroleum oil. Common examples of hydrocarbons that are used widely in our daily lives are methane (CH₄), ethane (C₂H6), ethylene (C₂H₄), acetylene (C₂H₂), cyclohexane (C₆H₁₂), etc

Such types of organic compounds are used in our homes as a source of energy. All other organic compounds are derived from hydrocarbons by the replacement of one or more hydrogen atoms with other atoms or groups of atoms.

Saturated Hydrocarbons

The organic molecules in which all the carbon atoms are linked by only single covalent bonds are called saturated hydrocarbons (alkanes or paraffin).

The general chemical formula of these types of compounds is C_nH_2n+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

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 C_nH_2(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 = C_nH_2n. Therefore, the molecular formula of cyclopentane = C₅H₁₀ and cyclohexane = C₆H₁₂.
• If the number of ring two, the general molecular formula = C_nH_2n−2.
• When the number of rings is three, the general molecular formula = C_nH_2n−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.

In organic chemistry, unsaturated types of hydrocarbon are further classified into the following two categories, alkenes or olefins and alkynes

Alkenes or Olefins

The unsaturated types of hydrocarbon 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 C_nH_2n. 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 C_nH_2n−2. Similarly, when three double bonds are present, the compounds are named tri-olefins or alkatrienes with the general molecular formula C_nH_2n−4.

Monocyclic Cycloalkenes

Monocyclic cycloalkenes are also unsaturated types of hydrocarbon 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 C_nH_2(n−r). Therefore, the molecular formula of cyclopropene = C₃H₄, cyclobutene = C₄H₆, cyclopentene = C₅H₈, cyclohexene = C₆H₁₀, and cycloheptene = C₇H₁₂.

Alkynes

In learning chemistry, alkynes are unsaturated types of hydrocarbon 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 C_nH_2n−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).