Saturated Hydrocarbon

What are Saturated Hydrocarbons?

A Saturated hydrocarbon is a hydrocarbon in which all the carbon-carbon bonds are single bonds. A hydrocarbon is an organic compound whose only constituents are carbon and hydrogen. As the name suggests, saturated hydrocarbons are hydrocarbons in which all the carbon atoms are bonded to four other atoms and are ‘saturated’, implying that no carbon-carbon multiple bonds exist in these organic compounds.

Generally, the term ‘saturated hydrocarbon’ is used to refer to alkanes – acyclic hydrocarbons containing only sp3 hybridized carbon atoms. The general formula of an alkane is CnH2n+2. An illustration describing the structure of a propane molecule (C3H8) is provided below.

Saturated Hydrocarbon

It can be observed that a propane molecule is ‘saturated’ with hydrogen atoms and cannot accommodate any more in the parent chain. A few other examples of saturated hydrocarbons are listed below.

  • Butane (C4H10)
  • Octane (C8H18)
  • Cyclohexane (C6H12)
  • Cyclopropane (C3H6)

Cycloalkanes are the alkanes that have a monocyclic ring structure. Since all the carbon-carbon bonds in cycloalkanes are single bonds, they are considered to be saturated hydrocarbons. Therefore, the general formula of a saturated hydrocarbon can be written as CnH(2n + 2 – 2r), where ‘r’ is the total number of rings in the molecule.

Difference Between Saturated and Unsaturated Hydrocarbon

Unsaturated hydrocarbons feature at least one double or triple bond between two adjacent carbon atoms. The key differences between saturated and unsaturated hydrocarbons are tabulated below.

Saturated Hydrocarbon Unsaturated Hydrocarbon
All carbon atoms are sp3 hybridized in these compounds. They contain sp2 or sp hybridized carbons.
Contain more hydrogen atoms than the corresponding unsaturated hydrocarbons. Contain fewer hydrogens than the corresponding saturated hydrocarbon.
Examples include alkanes and cycloalkanes. Examples include alkenes, alkynes, and aromatic hydrocarbons.
They have a relatively low chemical reactivity They are more reactive than their saturated counterparts.
They generally burn with a blue flame They generally burn with a sooty flame.

Types of Saturated Hydrocarbons

A saturated hydrocarbon can have a linear, branched, or a ring-shaped structure and can, therefore, be classified into one of the following types:

  1. Alkanes
  2. Cycloalkanes

It is important to note that even polycyclic alkanes (alkanes with several rings in their structures) are also categorized as cycloalkanes and are, therefore, a type of saturated hydrocarbons.

Alkanes

Alkanes can feature a linear or a branched carbon chain in their structures. All the carbon atoms in these saturated hydrocarbons are sp3 hybridized. The melting point and the boiling point of an alkane is related to the length of its carbon chain. The longer the chain, the higher the melting or boiling point. This is because molecules having long carbon chains have high molecular weights.

At standard temperatures, alkanes containing up to four carbon atoms are gases and those containing 5 to 17 carbon atoms are liquid. Alkanes that have more than 18 carbon atoms are solids at room temperature.

All alkanes containing more than 3 carbon atoms can exhibit chain isomerism. An illustration describing the possible chain isomers of butane (C4H10) is provided below.

Isomerism in Saturated Hydrocarbons

The number of possible chain isomers for an alkane depends on the total number of carbon atoms in it. For example, butane has only 2 chain isomers but octane (C8H18) has a total of 18 possible chain isomers.

Cycloalkanes

  • Cycloalkanes feature a ring-shaped arrangement of sp3 hybridized carbon atoms. However, the ring in these saturated hydrocarbons can branch into side chains.
  • The physical properties of cycloalkanes are somewhat similar to those of alkanes.
  • The melting and boiling points of cycloalkanes are generally higher than the alkanes containing the same number of carbon atoms.
  • Owing to their structures, cycloalkanes are subject to ring strain. Since cyclopropane has a carbon-carbon bond angle of 60o, it has the highest ring strain among all cycloalkanes.

What are the Uses of Saturated Hydrocarbons?

Alkanes are widely used as fuels, heating oils, and as solvents. A few other uses of saturated hydrocarbons are listed below.

  • Methane, the simplest alkane, is used as a fuel in several automobiles, water heaters, and ovens. In its highly refined form, liquid methane can also serve as rocket fuel.
  • Several cryogenic refrigeration systems use ethane as a refrigerant. It is also used in the production of ethylene.
  • The propellant used in several aerosol sprays is a saturated hydrocarbon known as propane. This compound is also used as a fuel for hot air balloons.
  • Octane is a very important component of gasoline since it helps prevent engine damage.
  • Cycloalkanes also find use in motor fuels, diesel, petroleum gas, and other heavy oils.
  • The manufacture of rubber and nylon also involve the use of cycloalkanes.

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