Organic chemistry is a major branch of chemistry comprising the study of carbon compounds containing hydrogen (simple carbon compounds such as carbon dioxide being usually deemed inorganic). This apparently specialized field is in fact wide and varied, because of carbon's almost unique ability to form linked chains of atoms to any length and complexity; far more organic compounds are known than inorganic.
Organic compounds form the basic stuff of living tissue (see also biochemistry), and until the mid-19th century, when organic syntheses were achieved, a "vital force" was thought necessary to make them. The 19th-century development of quantitative analysis by Justus Liebig and Jean Baptiste Dumas, and of structural theory by Stanislao Cannizzaro and Friedrich Kekulé, laid the basis for modern organic chemistry. Organic compounds are classified as aliphatic, alicyclic, aromatic, and heterocyclic compounds, according to the structure of the skeleton of the molecule, and are further subdivided in terms of the functional groups present.