Definitions

organometallic compound

organometallic compound

Any member of a class of substances containing at least one metal-to-carbon bond in which the carbon is part of an organic group. Most organometallic compounds are solids, although some are liquids and others are gases. While some organometallic compounds are stable, those containing electropositive elements, such as lithium, sodium, or aluminum, are spontaneously flammable and highly toxic. Organometallic compounds may form covalent bonds, in which electrons are shared equally between two atoms; multicentre covalent bonds, in which an electron pair is shared between more than two atoms; and ionic bonds, in which the electron pair is donated by only one atom. Polar organometallic compounds (one end of the compound is more negative than the other end) are formed as a result of covalent bonding in which there exists an unequal sharing of electrons between a metal and carbon atom. Polar organometallic compounds are valuable in the synthesis of certain materials and chemicals. For example, alkylaluminum is reacted with titanium salts to catalyze the polymerization of unsaturated hydrocarbons. This reaction is commonly used to catalyze the polymerization of ethylene to polyethylene, a type of plastic. Organometallic compounds containing tin are used as pharmaceuticals, pesticides, and fire retardants. Examples of well-characterized organometallic compounds include tetracarbonylnickel, Ni(CO)4, a volatile nickel compound used in the purification of nickel, and ferrocene, Fe(C5H5)2, a remarkably stable compound in which an iron atom is “sandwiched” between two hydrocarbon rings.

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An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic. The division between "organic" and "inorganic" carbon compounds while "useful in organizing the vast subject of chemistry...is somewhat arbitrary".

Organic chemistry is the science concerned with all aspects of organic compounds. Organic synthesis is the methodology of their preparation.

History

The name "organic" is historical, dating back to the 19th century, when it was believed that organic compounds could only be synthesized in living organisms through vis vitalis - the "life-force". The theory that organic compounds were fundamentally different from those that were "inorganic", that is, not synthesized through a life-force, was disproved with the synthesis of urea, an "organic" compound by definition of its known occurrence only in the urine of living organisms, from potassium cyanate and ammonium sulfate by Friedrich Wöhler in the Wöhler synthesis. The kinds of carbon compounds 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.

Classification

See Organic chemistry#Classification of organic substances

Organic compounds may contain atoms of further elements, so-called heteroatoms. Organometallic compounds constitute a further subsection, characterized by covalent bonds between organic carbon and a metal.

There is also a large number of inorganic carbon compounds to distinguish from organic compounds.

Natural compounds

An important subset of organic compounds is still extracted from natural sources because they would be far too expensive to be produced 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 organisms.

Further compounds of prime importance in biochemistry are antigens, carbohydrates, enzymes, hormones, lipids and fatty acids, neurotransmitters, nucleic acids, proteins, peptides and amino acids, vitamins and fats and oils.

Synthetic compounds

Many polymers, including all plastics are organic compounds.

Nomenclature

The IUPAC nomenclature of organic compounds slightly differs from the CAS nomenclature.

Databases

  • The CAS database is the most comprehensive repository for data on organic compounds. The search tool SciFinder is offered .
  • The Beilstein database contains information on 9.8 million substances, covers the scientific literature from 1771 to the present, and is today accessible via CrossFire. Structures and a large diversity of physical and chemical properties is available for each substance, with reference to original literature.
  • PubChem contains 18.4 million entries on compounds and especially covers the field of medicinal chemistry.

There is a great number of more specialized databases for diverse branches of organic chemistry.

Structure determination

''See Structure determination

Today, the main tools are proton and carbon-13 NMR spectroscopy and X-ray crystallography.

See also

References

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