Organic compounds contain carbon, and almost all organic compounds contain hydrogen, with many also comprised of additional atoms of nitrogen, oxygen or sulfur. Not all compounds that contain carbon, however, can be considered organic. Metallic alloys that contain carbon, such as steel for example, would not be universally considered organic, mainly because they are not involved in biological processes.
A commonly accepted definition of an organic compound is that it is a compound which is involved in a biochemical process and which plays a role in the survival of a living organism. This view of organic compounds dates back to the classical belief that certain substances were vital to life and were only possessed or made by living organisms. This belief was altered in the 1820s when Friedrich Wohler demonstrated that two compounds found in living organisms, oxalic acid and urea, could be created in a laboratory.
Many fields of modern chemistry have since considered any compound containing a significant degree of the element carbon to be an organic compound, even though many compounds containing carbon have no relevance to biological processes. Organic compounds, for example, play an important role in non-biological fields such as petrochemicals, adhesives and plastics.
The greater majority of organic compounds are molecular rather than ionic compounds and can be effectively synthesized outside of a living organism. Some of the most common organic compounds are carbohydrates, proteins, vitamins, enzymes, polymers and many forms of fuel.