Methane, CH4; it is one of the simplest organic compounds.
In chemistry, an organic compound is generally any chemical compound that contains carbon. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Study of the properties and synthesis of organic compounds is the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonates and cyanides), along with a handful of other exceptions (e.g., carbon dioxide), are not classified as organic compounds and are considered inorganic. No consensus exists among chemists on precisely which carbon-containing compounds are excluded, making the definition of an organic compound elusive. Although organic compounds only make up a small percentage of the Earth's crust, they are of central importance because all known life is based on organic compounds. Most synthetically produced organic compounds are ultimately derived from petrochemicals consisting mainly of hydrocarbons.
For historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon (for example, CO and CO2), and cyanides are considered inorganic. Allotropes of carbon, such as diamond and graphite, are also excluded because they are simple substances composed of only a single element and therefore are not chemical compounds at all.
Organic chemistry is the science concerned with all aspects of organic compounds. Organic synthesis is the methodology of their preparation.