Organic chemistry
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Organic chemistry is a subdiscipline within
The range of chemicals studied in organic chemistry includes
In addition, contemporary research focuses on organic chemistry involving other
Organic compounds form the basis of all
History
Before the 18th century, chemists generally believed that compounds obtained from living organisms were endowed with a vital force that distinguished them from inorganic compounds. According to the concept of vitalism (vital force theory), organic matter was endowed with a "vital force".[4] During the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 Michel Chevreul started a study of soaps made from various fats and alkalis. He separated the 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 Wöhler produced the organic chemical urea (carbamide), a constituent of urine, from inorganic starting materials (the salts potassium cyanate and ammonium sulfate), in what is now called the Wöhler synthesis. Although Wöhler himself was cautious about claiming he had disproved vitalism, this was the first time a substance thought to be organic was synthesized in the laboratory without biological (organic) starting materials. The event is now generally accepted as indeed disproving the doctrine of vitalism.[5]
In 1856,
A crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently in 1858 by both
The era of the
Early examples of organic reactions and applications were often found because of a combination of luck and preparation for unexpected observations. The latter half of the 19th century however witnessed systematic studies of organic compounds. The development of synthetic indigo is illustrative. The production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the synthetic methods developed by Adolf von Baeyer. In 2002, 17,000 tons of synthetic indigo were produced from petrochemicals.[14]
In the early part of the 20th century, polymers and enzymes were shown to be large organic molecules, and petroleum was shown to be of biological origin.
The multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of complex natural compounds increased in complexity to glucose and terpineol. For example, cholesterol-related compounds have opened ways to synthesize complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as lysergic acid and vitamin B12.[15]
The discovery of
The majority of chemical compounds occurring in biological organisms are carbon compounds, so the association between organic chemistry and biochemistry is so close that biochemistry might be regarded as in essence a branch of organic chemistry. Although the history of biochemistry might be taken to span some four centuries, fundamental understanding of the field only began to develop in the late 19th century and the actual term biochemistry was coined around the start of 20th century. Research in the field increased throughout the twentieth century, without any indication of slackening in the rate of increase, as may be verified by inspection of abstraction and indexing services such as BIOSIS Previews and Biological Abstracts, which began in the 1920s as a single annual volume, but has grown so drastically that by the end of the 20th century it was only available to the everyday user as an online electronic database.[16]
Characterization
Since organic compounds often exist as
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.[17] Listed in approximate order of utility, the chief analytical methods are:
- 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.
- fragmentation patterns, its structure. High-resolution mass spectrometry can usually identify the exact formula of a compound and is used in place 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 can be useful for determining molecular geometry when a single crystal of the material is available. Highly efficient hardware and software allows a structure to be determined within hours of obtaining a suitable crystal.
Traditional spectroscopic methods such as
Properties
The physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information includes a melting point, boiling point, solubility, and index of refraction. Qualitative properties include odor, consistency, and color.
Melting and boiling properties
Organic compounds typically melt and many boil. In contrast, while inorganic materials generally can be melted, many do not boil, and instead tend to degrade. 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,
Solubility
Neutral organic compounds tend to be
Solid state properties
Various specialized properties of
Nomenclature
The names of organic compounds are either systematic, following logically from a set of rules, or nonsystematic, following various traditions. Systematic nomenclature is stipulated by specifications from
Nonsystematic nomenclature is simpler and unambiguous, at least to organic chemists. Nonsystematic names do not indicate the structure of the compound. They are common for complex molecules, which include most natural products. Thus, the informally named
With the increased use of computing, other naming methods have evolved that are intended to be interpreted by machines. Two popular formats are
Structural drawings
Organic molecules are described more commonly by drawings or
History
By 1880 an explosion in the number of chemical compounds being discovered occurred assisted by new synthetic and analytical techniques. Grignard described the situation as "chaos le plus complet" (complete chaos) due to the lack of convention it was possible to have multiple names for the same compound. This led to the creation of the Geneva rules in 1892.[18]
Classification of organic compounds
Functional groups
The concept of functional groups is central in organic chemistry, both as a means to classify structures and for predicting properties. A functional group is a molecular module, and the reactivity of that functional group is assumed, within limits, to be the same in a variety of molecules. Functional groups can have a decisive influence on the chemical and physical properties of organic compounds. Molecules are classified based on their functional groups. Alcohols, for example, all have the subunit C-O-H. All alcohols tend to be somewhat hydrophilic, usually form esters, and usually can be converted to the corresponding halides. Most functional groups feature heteroatoms (atoms other than C and H). Organic compounds are classified according to functional groups, alcohols, carboxylic acids, amines, etc.[19] Functional groups make the molecule more acidic or basic due to their electronic influence on surrounding parts of the molecule.
As the pKa (aka basicity) of the molecular addition/functional group increases, there is a corresponding dipole, when measured, increases in strength. A dipole directed towards the functional group (higher pKa therefore basic nature of group) points towards it and decreases in strength with increasing distance. Dipole distance (measured in Angstroms) and steric hindrance towards the functional group have an intermolecular and intramolecular effect on the surrounding environment and pH level.
Different functional groups have different pKa values and bond strengths (single, double, triple) leading to increased electrophilicity with lower pKa and increased nucleophile strength with higher pKa. More basic/nucleophilic functional groups desire to attack an electrophilic functional group with a lower pKa on another molecule (intermolecular) or within the same molecule (intramolecular). Any group with a net acidic pKa that gets within range, such as an acyl or carbonyl group is fair game. Since the likelihood of being attacked decreases with an increase in pKa,
Aliphatic compounds
The aliphatic hydrocarbons are subdivided into three groups of homologous series according to their state of saturation:
- alkanes (paraffins): aliphatic hydrocarbons without any double or triple bonds, i.e. just C-C, C-H single bonds
- alkenes (olefins): aliphatic hydrocarbons that contain one or more double bonds, i.e. di-olefins (dienes) or poly-olefins.
- alkynes (acetylenes): aliphatic hydrocarbons which have one or more triple bonds.
The rest of the group is classified according to the functional groups present. Such compounds can be "straight-chain", branched-chain or cyclic. The degree of branching affects characteristics, such as the
Both saturated (
Aromatic compounds
Heterocyclic compounds
The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter, the ring is termed a
Heterocycles are commonly found in a wide range of products including aniline dyes and medicines. Additionally, they are prevalent in a wide range of biochemical compounds such as
Rings can fuse with other rings on an edge to give polycyclic compounds. The purine nucleoside bases are notable polycyclic aromatic heterocycles. Rings can also fuse on a "corner" such that one atom (almost always carbon) has two bonds going to one ring and two to another. Such compounds are termed spiro and are important in several natural products.
Polymers
One important property of carbon is that it readily forms chains, or networks, that are linked by carbon-carbon (carbon-to-carbon) bonds. The linking process is called polymerization, while the chains, or networks, are called polymers. The source compound is called a monomer.
Two main groups of polymers exist
Biomolecules
See also: peptide synthesis, oligonucleotide synthesis and carbohydrate synthesis.
Small molecules
In pharmacology, an important group of organic compounds is small molecules, also referred to as 'small organic compounds'. In this context, a small molecule is a small organic compound that is biologically active but is not a polymer. In practice, small molecules have a molar mass less than approximately 1000 g/mol.
Fullerenes
Fullerenes and carbon nanotubes, carbon compounds with spheroidal and tubular structures, have stimulated much research into the related field of materials science. The first fullerene was discovered in 1985 by Sir Harold W. Kroto of the United Kingdom and by Richard E. Smalley and Robert F. Curl Jr., of the United States. Using a laser to vaporize graphite rods in an atmosphere of helium gas, these chemists and their assistants obtained cagelike molecules composed of 60 carbon atoms (C60) joined by single and double bonds to form a hollow sphere with 12 pentagonal and 20 hexagonal faces—a design that resembles a football, or soccer ball. In 1996 the trio was awarded the Nobel Prize for their pioneering efforts. The C60 molecule was named buckminsterfullerene (or, more simply, the buckyball) after the American architect R. Buckminster Fuller, whose geodesic dome is constructed on the same structural principles.
Others
Organic compounds containing bonds of carbon to nitrogen, oxygen and the halogens are not normally grouped separately. Others are sometimes put into major groups within organic chemistry and discussed under titles such as
Organic reactions
The basic reaction types are: addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and redox reactions. An example of a common reaction is a substitution reaction written as:
where X is some functional group and Nu is a nucleophile.
The number of possible organic reactions is infinite. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens in sequence—although the detailed description of steps is not always clear from a list of reactants alone.
The stepwise course of any given reaction mechanism can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition through intermediates to final products.
Organic synthesis
Synthetic organic chemistry is an
Strategies to design a synthesis include
See also
References
- ^ ISBN 0-19-927029-5.
- ^ Elschenbroich, C. (2006) Organometallics 3rd Ed., Wiley-VCH
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- ISBN 978-0-08-037941-8.
- ^ Henry Marshall Leicester; Herbert S. Klickstein (1951). A Source Book in Chemistry, 1400-1900. Harvard University Press. p. 309.
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- ^ "August Kekulé and Archibald Scott Couper". Science History Institute. June 2016. Retrieved 20 March 2018.
- ISBN 978-93-85998-89-8.
- ^ Roberts, Laura (7 December 2010) History of Aspirin. The Telegraph
- PMID 18679046.
- ^ "Paul Ehrlich, the Rockefeller Institute, and the first targeted chemotherapy". Rockefeller University. Retrieved 3 Aug 2012.
- ^ "Paul Ehrlich". Science History Institute. June 2016. Retrieved 20 March 2018.
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- ISBN 978-0-471-72091-1
- ^ "The pKa Table Is Your Friend". Master Organic Chemistry. 2010-06-18. Retrieved 2021-03-16.
- ^ "industrial polymers, chemistry of." Encyclopædia Britannica. 2006
External links
- MIT.edu, OpenCourseWare: Organic Chemistry I
- HaverFord.edu, Organic Chemistry Lectures, Videos and Text
- Organic-Chemistry.org, Organic Chemistry Portal – Recent Abstracts and (Name)Reactions
- Orgsyn.org, Organic Chemistry synthesis journal
- Clutchprep.com, Organic Chemistry Video Lectures and Practice Problems
- Khanacademy.org, Khan Academy - Organic Chemistry