Organic chemistry is a discipline within chemistry that involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of carbon-based compounds, hydrocarbons, and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as wellas phosphorus, silicon and sulfur.
Organic compounds are structurally diverse, and the range of application of organic compounds is enormous. They form the basis of, or are important constituents of many products (plastics, drugs, petrochemicals, food, explosives, paints, to name but a few) and, with very few exceptions, they form the basis of all earthly life processes.
Organicchemistry, like all areas of science, evolves with particular waves of innovation. These innovations are motivated by practical considerations as well as theoretical innovations. The area is, however, underpinned financially by the very large applications in biochemistry, polymer science, pharmaceutical chemistry, and agrochemicals.
Since organic compounds often exist as mixtures, avariety of techniques have also been developed to assess purity, especially important being chromatography techniques such as HPLC and gas chromatography. Traditional methods of separation include distillation, crystallization, and solvent extraction.
Organic compounds were traditionally characterized by a variety of chemical tests, called "wet methods," but such tests have been largely displaced byspectroscopic or other computer-intensive methods of analysis. Listed in approximate order of utility, the chief analytical methods are:
* Nuclear magnetic resonance (NMR) spectroscopy is the most commonly used technique, often permitting complete assignment of atom connectivity and even stereochemistry using correlation spectroscopy. The principal constituent atoms of organic chemistry -hydrogen and carbon - exist naturally with NMR-responsive isotopes, respectively 1H and 13C.
* Elemental analysis: A destructive method used to determine the elemental composition of a molecule. See also mass spectrometry, below.
* Mass spectrometry indicates the molecular weight of a compound and, from the fragmentation patterns, its structure. High resolution mass spectrometry canusually identify the exact formula of a compound and is used in lieu of elemental analysis. In former times, mass spectrometry was restricted to neutral molecules exhibiting some volatility, but advanced ionization techniques allow one to obtain the "mass spec" of virtually any organic compound.
* Crystallography is an unambiguous method for determining molecular geometry, the proviso being thatsingle crystals of the material must be available and the crystal must be representative of the sample. Highly automated software allows a structure to be determined within hours of obtaining a suitable crystal.
Traditional spectroscopic methods such as infrared spectroscopy, optical rotation, UV/VIS spectroscopy provide relatively nonspecific structural information but remain in use forspecific classes of compounds.
Additional methods are described in the article on analytical chemistry.
Physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information include melting point, boiling point, and index of refraction. Qualitative properties include odor, solubility, and color.
Melting and boilingproperties
In contrast to many inorganic materials, organic compounds typically melt and many boil. In earlier times, the melting point (m.p.) and boiling point (b.p.) provided crucial information on the purity and identity of organic compounds. The melting and boiling points correlate with the polarity of the molecules and their molecular weight. Some organic compounds, especially symmetrical ones,...