Organic chemistry is a subdiscipline within
chemistry involving 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 well as
phosphorus,
silicon and
sulfur.
History
In the early nineteenth century, chemists generally believed that compounds obtained from living organisms were too complex to be obtained
synthetically. According to the concept of
vitalism, organic matter was endowed with a "vital force". They named these compounds "organic" and directed their investigations toward inorganic materials that seemed more easily studied.
[citation needed]During the first half of the nineteenth century, scientists realized that organic compounds can be synthesized in the laboratory. Around 1816
Michel Chevreul started a study of
soaps made from various
fats and
alkalis. He separated the different acids that, in combination with the alkali, produced the soap. Since these were all individual compounds, he demonstrated that it was possible to make a chemical change in various fats (which traditionally come from organic sources), producing new compounds, without "vital force". In 1828
Friedrich Wöhlerproduced the organic chemical
urea (carbamide), a constituent of
urine, from the inorganic
ammonium cyanate NH
4CNO, in what is now called the
Wöhler synthesis. Although Wöhler was always cautious about claiming that he had disproved the theory of vital force, this event has often been thought of as a turning point.
In 1856
William Henry Perkin, while trying to manufacture
quinine, accidentally manufactured the organic
dye now known as
Perkin's mauve. Through its great financial success, this discovery greatly increased interest in organic chemistry.
The crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently and simultaneously by
Friedrich August Kekule and
Archibald Scott Couper in 1858. Both men suggested that
tetravalent carbon atoms could link to each other to form a carbon lattice, and that the detailed patterns of atomic bonding could be discerned by skillful interpretations of appropriate chemical reactions.
The history of organic chemistry continued with the discovery of
petroleum and its separation into
fractions according to boiling ranges. The conversion of different compound types or individual compounds by various chemical processes created the petroleum chemistry leading to the birth of the
petrochemical industry, which successfully manufactured artificial
rubbers, the various organic
adhesives, the property-modifying petroleum additives, and
plastics.
The
pharmaceutical industry began in the last decade of the 19th century when acetylsalicylic acid (more commonly referred to as
aspirin) manufacture was started in Germany by
Bayer. The first time a drug was systematically improved was with
arsphenamine (Salvarsan). Numerous derivatives of the dangerously toxic
atoxyl were examined by
Paul Ehrlich and his group, and the compound with best effectiveness and toxicity characteristics was selected for production.
Although early examples of organic reactions and applications were often
serendipitous, the latter half of the 19th century witnessed highly systematic studies of organic compounds. Beginning in the 20th century, progress of organic chemistry allowed the synthesis of highly complex molecules via multistep procedures. Concurrently, polymers and enzymes were understood to be large organic molecules, and petroleum was shown to be of biological origin. The process of finding new synthesis routes for a given compound is called total synthesis.
Total synthesis of complex natural compounds started with
urea, increased in complexity to
glucose and
terpineol, and in 1907, total synthesis was commercialized the first time by
Gustaf Komppa with
camphor. Pharmaceutical benefits have been substantial, for example
cholesterol-related compounds have opened ways to synthesis of complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increasing, with examples such as
lysergic acid and
vitamin B12. Today's targets feature tens of
stereogenic centers that must be synthesized correctly with
asymmetric synthesis.
Biochemistry, the chemistry of living organisms, their structure and interactions
in vitro and inside living systems, has only started in the 20th century, opening up a new chapter of organic chemistry with enormous scope. Biochemistry, like organic chemistry, primarily focuses on compounds containing carbon.
[edit]Characterization
Organic compounds were traditionally characterized by a variety of chemical tests, called "wet methods," but such tests have been largely displaced by spectroscopic or other computer-intensive methods of analysis.
[4] 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 usingcorrelation 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 can usually 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 that single 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.
[edit]Properties
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, consistency, solubility, and color.
[edit]Melting and boiling properties
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, sublime, that is they evaporate without melting. A well known example of a sublimable organic compound is
para-dichlorobenzene, the odiferous constituent of mothballs. Organic compounds are usually not very stable at temperatures above 300 °C, although some exceptions exist.
[edit]Solubility
[edit]Solid state properties
