Organic Chemistry: Hydrocarbons

Overview

Hydrocarbons are a large class of organic compounds made up solely of carbon and hydrogen atoms.
They are the primary constituents of fossil fuels, natural gas, and many other important substances.

Types of Hydrocarbons

There are three main types of hydrocarbons which include alkanes, alkenes, and alkynes.

Alkanes

Alkanes are the simplest type of hydrocarbons. They are also referred to as saturated hydrocarbons.
In alkanes, all carbon-carbon bonds are single bonds, which means each carbon atom is bonded with the maximum number of hydrogen atoms. It makes them ‘saturated’.
Alkanes have a general formula of CnH2n+2 where ‘n’ is the number of carbon atoms.
The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10).

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond. This gives them different chemical properties to alkanes.
Alkenes are ‘unsaturated’ because they have fewer hydrogen atoms than equivalent alkanes.
The general formula for alkenes is CnH2n.
The first three alkenes are ethene (C2H4), propene (C3H6) and butene (C4H8).

Alkynes

Alkynes are hydrocarbons that consist at least one carbon-carbon triple bond. They are also considered ‘unsaturated’.
The general formula for alkynes is CnH2n-2.
The simplest alkyne is ethyne (C2H2) also known as acetylene.

Properties of Hydrocarbons

Physical properties such as boiling point and melting point vary with the chain length and the type of bond present in hydrocarbons. They generally increase with increasing molecular weight.
The alkanes are generally chemically unreactive except when exposed to strong oxidising agents or ultraviolet light.
In contrast, alkenes and alkynes, because of the presence of double and triple bonds respectively, are much more reactive.

Uses of Hydrocarbons

Hydrocarbons have a wide range of uses. They can be used as fuels (like petrol and diesel), in plastics production, as solvents, in the synthesis of industrial chemicals and much more.

Reactions of Hydrocarbons

One of the most important reactions of hydrocarbons is combustion. During combustion, hydrocarbons react with oxygen to produce carbon dioxide, water and energy.
Other important reactions include substitution reactions (for alkanes), addition reactions and polymerisation (for alkenes), and hydrogenation reactions (for alkenes and alkynes).