An<unk>  is any member of a large class of chemical<unk> s whose molecules contain carbon; for historical reasons discussed below, a few types of<unk> s such as carbonates, carbon oxides and cyanides, as well as elemental carbon are considered inorganic.The study of<unk> s is termed<unk>  chemistry, and since it is a vast collection of chemicals (over half of all known chemical<unk> s), systems have been devised to classify<unk> s. A few of the<unk>  classes based on the functional groups they carry are as follows:
Acid anhydrides
Acyl halides
Alcohols
Aldehydes
Alkanes
Alkenes
Alkynes
Amides
Amines
Aromatics
Azo<unk> s
Carboxylic acids
Esters
Ethers
Haloalkanes
Imines
Ketones
Nitriles
Nitro<unk> s
Organometallic<unk> s
Phenols
Polymers, including all plastics
Thiols
Many<unk> s are also of prime importance in biochemistry:
Antigens
Polysaccharides, carbohydrates and sugars
Enzymes
Hormones
Lipids and fatty acids
Neurotransmitters
Nucleic acids
Proteins, peptides and amino acids
Vitamins
The name<unk> " is a historical name, dating back to 19th century, when it was believed that<unk> s could only be synthesised in living<unk> ms through vis vitalis - the "life-force".  The theory that<unk> s were fundamentally different from those that were "inorganic", that is, not synthesized through a life-force, was disproved with the synthesis of urea, an<unk> "<unk>  by definition of its known occurrence only in the urine of living<unk> ms, from potassium cyanate and ammonium sulfate by Friedrich Wöhler in the Wöhler synthesis. The kinds of carbon<unk> s that are still traditionally considered inorganic are those that were considered inorganic before Wöhler's time; that is, those which came from "inorganic" (i.e., lifeless) sources such as minerals.
Most pure<unk> s today are artificially produced, although an important subset are still extracted from natural sources because they would be far too expensive to produce artificially. Examples include most sugars, some alkaloids and terpenoids, certain nutrients such as vitamin B12, and in general, those natural products with large or stereoisometrically complicated molecules which are present in reasonable concentrations in living<unk> ms.
The statistical analysis of chemical structures is called chemical informatics. The Beilstein database contains a large collection of<unk> s. A cheminformatics study involving 5.9 million substances and 6.5 million reactions showed that the<unk>  universe consists of a core of around 200,000 molecules strongly connected to each other and a large periphery (3.6 million molecules) around it. Core and periphery are surrounded by a group of non-connected small islands containing 1.2 million molecules, a model resembling the world wide web. More key statistics:
The core molecules (only 3.5% of the total) are involved in 35% of all reactions giving rise to 60% of all molecules.
The average distance between two molecules in the core is 8.4 synthetic steps and 95% of all connecting reactions are fewer than 15 steps. Any molecule in the periphery can be reached by one from the core in fewer than 3 steps.
The relative size of the core peaked in 1880 and has since then declined.
The core contains 70% of the top 200 industrial chemicals.
An optimised chemical inventory of 300 chemicals for a hypothetical chemical company allows the synthesis of up to 1.2 million<unk> s and contains 10 Wittig reagents, 6 Grignard reagents, 2 DNA building blocks and 18 aromatic aldehydes.
Organic compound
Metal
Chemical substance
Biopolymer
Biological pigment
Biomolecule
Polycyclic compound
Phytochemical