Organic compounds are a class of complex molecules that are characterized by their use of carbon as a molecular backbone. Carbon is able to bond with up to four other atoms, which makes it ideal for building up the complicated molecules typical of organic chemistry.
All organic compounds make use of carbon in some way, but not all carbon-based molecules are regarded as organic. Carbon dioxide and carbon monoxide, for example, are relatively simple and are usually regarded as outside of the organic group despite their use of carbon.
Apart from their complexity, organic compounds are of interest because of their role in the chemistry of life on Earth. All living things are built from organic compounds, and every known biological process depends on their reactions. Organic compounds also play a big role in the world's energy economy. Much of the world's energy is derived from the controlled burning of organic compounds, known as hydrocarbons, to generate electricity and power vehicles. Hydrocarbons are also used to produce synthetic materials such as plastic.
Some organic compounds occur naturally and can be extracted from their source in an almost pure form. Rubber is an example of a naturally occurring organic compound. Other compounds are considered synthetic and have to be built up from other molecules, such as most polymers.