Organic Compounds - Structure and Reactions – iGCSE Chemistry (Triple) OxfordAQA Revision

Organic Compounds - Structure and Reactions

The study of carbon-containing compounds is known as organic chemistry.
Organic compounds contain carbon atoms, which can bond to other carbon atoms to form chains and rings of varying lengths and complexities.
Hydrocarbons are organic compounds that contain only carbon and hydrogen.
There are three main types of hydrocarbons: alkanes, alkenes and alkynes. Each has a different type of carbon-to-carbon bond: single, double, and triple, respectively.

Alkanes are hydrocarbons with single bonds only. They follow the general formula CnH2n+2.
The presence of only single bonds makes alkanes saturated hydrocarbons. They are less reactive compared to other hydrocarbons.
The first four alkanes are methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10).

Alkenes are hydrocarbons containing a double bond. They follow the general formula CnH2n.
The double bond makes alkenes more reactive, hence they are unsaturated hydrocarbons.
The first two alkenes are ethene (C2H4) and propene (C3H6).

Alkynes are hydrocarbons that contain a triple bond. They follow the general formula CnH2n-2.
Due to the presence of the triple bond, alkynes are also unsaturated hydrocarbons and are highly reactive.
The first two alkynes are ethyne (C2H2) and propyne (C3H4).

Hydrocarbons, and organic compounds in general, can undergo various types of reactions, including combustion, addition, substitution, polymerisation, and cracking.

In the presence of oxygen, hydrocarbons combust to produce carbon dioxide and water. Combustion reactions are exothermic, releasing energy.
If insufficient oxygen is available, incomplete combustion may occur, producing carbon monoxide (a poisonous gas) or even carbon soot.

Alkenes and alkynes, being unsaturated, can undergo addition reactions where molecules, such as hydrogen or halogens, add across the double or triple bond. This changes the alkene or alkyne to an alkane.

Alkanes, due to their single bonds, undergo substitution reactions. In these reactions, a hydrogen atom from the alkane is replaced by another atom, such as a halogen atom.

Many small organic molecules (monomers) can join together in a reaction known as polymerisation to form large molecules called polymers. One common example of this is the polymerisation of ethene to form poly(ethene), commonly known as polythene.

The process of breaking down large hydrocarbons into smaller, more useful ones is called cracking. This can be achieved by either thermal decomposition or by using a catalyst.
Cracking can result in the formation of both alkanes and alkenes.

Organic compounds are of immense importance as they form the basis of many items we use daily, such as fuels, plastics, medicines, and fabrics.
Experiments and advancements in organic chemistry play an integral role in finding solutions to environmental concerns, such as reducing carbon emissions and developing bio-degradable materials.