For historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates (excluding carbonate esters), simple oxides of carbon (for example, CO and carbon dioxide|) and cyanides are generally considered inorganic compounds. Different forms (allotropes) of pure carbon, such as diamond, graphite, fullerenes and carbon nanotubes are also excluded because they are simple substances composed of a single element and so not generally considered chemical compounds.
The word "organic" in this context does not mean "natural".