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Encyclopedia > Isomer

In chemistry, isomers are molecules with the same chemical formula and often with the same kinds of chemical bonds between atoms, but in which the atoms are arranged differently (analogous to a chemical anagram). Many isomers share similar if not identical properties in most chemical contexts. This should not be confused with a nuclear isomer, which involves a nucleus at different states of excitement. Image File history File links Question_book-3. ... For other uses, see Chemistry (disambiguation). ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... For the game, see Anagrams. ... A nuclear isomer is a metastable or isomeric state of an atom caused by the excitation of a proton or neutron in its nucleus so that it requires a change in spin before it can release its extra energy. ...


A simple example of isomerism is given by propanol: it has the formula C3H8O (or C3H7OH) and two isomers propan-1-ol (n-propyl alcohol; I) and propan-2-ol (isopropyl alcohol; II) There are two isomers of propanol. ... For other uses, see Carbon (disambiguation). ... This article is about the chemistry of hydrogen. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... // Hydroxyl group The term hydroxyl group is used to describe the functional group -OH when it is a substituent in an organic compound. ... R-phrases , , S-phrases , , , , , Flash point 15 °C RTECS number UH8225000 Supplementary data page Structure and properties n, εr, etc. ... Isopropyl alcohol or isopropanol is a common name for 2-propanol, an alcohol commonly used for application to the skin, and popularly referred to as rubbing alcohol. ...

Note that the position of the oxygen atom differs between the two: it is attached to an end carbon in the first isomer, and to the center carbon in the second. The number of possible isomers increases rapidly as the number of atoms increases; for example the next largest alcohol, named butanol (C4H10O), has four different structural isomers. Image File history File links Structural_isomers. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... For other uses, see Carbon (disambiguation). ... Butanol or butyl alcohol (sometimes also called biobutanol when produced biologically), is an alcohol with a 4 carbon structure and the molecular formula of C4H10O. It is primarily used as a solvent, as an intermediate in chemical synthesis, and as a fuel. ...


In the example above it should also be noted that in both isomers all the bonds are single bonds; there is no type of bond that appears in one isomer and not in the other. Also the number of bonds is the same. From the structures of the two molecules it could be deduced that their chemical stabilities are liable to be identical or nearly so. Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 atmosphere...


There is, however, another isomer of C3H8O which has significantly different properties: methoxyethane (III). Notice that unlike the top two examples, the oxygen is connected to two carbons rather than to one carbon and one hydrogen. As it lacks a hydroxyl group, the above molecule is no longer considered an alcohol but is classified as an ether, and has chemical properties more similar to other ethers than to either of the above alcohol isomers. For other uses, see Carbon (disambiguation). ... This article is about the chemistry of hydrogen. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Methoxyethane, also known as methyl ethyl ether, is a colorless gaseous ether with a medicine-like odor. ... Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. ... This article is about a general class of chemical compounds. ...


Another example of isomers having very different properties can be found in certain xanthines. Theobromine is found in chocolate, but if one of the two methyl groups is moved to a different position on the two-ring core, the isomer is theophylline, used as a bronchodilator. Xanthines are a group of alkaloids that are commonly used for their effects as mild stimulants and as bronchodilators, notably in treating the symptoms of asthma. ... Theobromine, also known as xantheose,[1] is a bitter alkaloid of the cacao plant. ... For other uses, see Chocolate (disambiguation). ... In chemistry a methyl-group is a hydrophobic Alkyl functional group which is derived from methane (CH4). ... Theophylline is a methylxanthine drug used in therapy for respiratory diseases such as COPD or asthma under a variety of brand names. ... A bronchodilator is a medication intended to improve bronchial airflow. ...


Allene and propyne are examples of isomers containing different bond types. Allene contains two double bonds, while propyne contains one triple bond. Propan-1,2-diene is the simplest allene. ... Methylacetylene (propyne) is an alkyne with the chemical formula CH3C≡CH. It is a component of MAPP gas, which is commonly used in gas welding. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ...


Classification

The different types of isomers
The different types of isomers

There are two main forms of isomerism: structural isomerism and stereoisomerism. Image File history File links Isomerism. ... Image File history File links Isomerism. ... Structural isomerism (or constitutional isomerism) is a form of isomerism in which molecules with the same molecular formula have atoms bonded together in different orders, as opposed to stereoisomerism. ... Main article: stereochemistry Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ...


In structural isomers, the atoms and functional groups are joined together in different ways, as in the example of propyl alcohol above. This group includes chain isomerism whereby hydrocarbon chains have variable amounts of branching; position isomerism which deals with the position of a functional group on a chain; and functional group isomerism in which one functional group is split up into different ones. In organic chemistry, functional groups (or moieties) are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... Oil refineries are key to obtaining hydrocarbons; crude oil is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products. ...


In stereoisomers the bond structure is the same, but the geometrical positioning of atoms and functional groups in space differs. This class includes enantiomers where different isomers are non-superimposable mirror-images of each other, and diastereomers when they are not. Diastereomerism is again subdivided into conformational isomerism (conformers) when isomers can interconvert by chemical bond rotations and cis-trans isomerism when this is not possible. Note that although conformers can be referred to as having a diastereomeric relationship, the isomers over all are not diastereomers, since bonds in conformers can be rotated to make them mirror images. In chemistry, enantiomers (from the Greek ἐνάντιος, opposite, and μέρος, part or portion) are stereoisomers that are nonsuperimposable complete mirror images of each other, much as ones left and right hands are the same but opposite. ... Diastereomers (or diastereoisomers) are stereoisomers that are not enantiomers (mirror images of each other). ... Conformational isomerism is the phenomenon of molecules with the same structural formula but different conformations (conformers) of atoms about a rotating bond. ... Cis-2-butene Trans-2-butene In chemistry, geometric isomerism or cis-trans isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. ...


In skeletal isomers the main carbon chain is different between the two isomers. This type of isomerism is most identifiable in secondary and tertiary alcohol isomers.


Tautomers are structural isomers of the same chemical substance that spontaneously interconvert with each other, even when pure. They have different chemical properties, and consequently, distinct reactions characteristic to each form are observed. If the interconversion reaction is fast enough, tautomers cannot be isolated from each other. An example is when they differ by the position of a proton, such as in keto/enol tautomerism, where the proton is alternately on the carbon or oxygen. Tautomers are organic compounds that are interconvertible by a chemical reaction called tautomerization. ...


In food chemistry, medicinal chemistry and biochemistry, cis-trans isomerism is always considered. In medicinal chemistry and biochemistry, enantiomers are of particular interest since most changes in these types of isomers are now known to be meaningful in living organisms. Pharmaceutical and academic researchers have found chromatographical methods to reliably separate these from each other. On an industrial scale, however, these methods are rather costly and are mostly used to filter out the potentially harmful or biologically inactive enantiomer. Food chemistry is the study of chemical processes and interactions of all biological and non-biological components of foods. ... Medicinal or pharmaceutical chemistry is a scientific discipline at the intersection of chemistry and pharmacy involved with designing, synthesizing and developing pharmaceutical drugs. ... Biochemistry (from Greek: , bios, life and Egyptian kēme, earth[1]) is the study of the chemical processes in living organisms. ... Cis-2-butene Trans-2-butene In chemistry, geometric isomerism or cis-trans isomerism is a form of stereoisomerism and describes the orientation of functional groups at the ends of a bond around which no rotation is possible. ... Medicinal or pharmaceutical chemistry is a scientific discipline at the intersection of chemistry and pharmacy involved with designing, synthesizing and developing pharmaceutical drugs. ... Biochemistry (from Greek: , bios, life and Egyptian kēme, earth[1]) is the study of the chemical processes in living organisms. ... In chemistry, enantiomers (from the Greek ἐνάντιος, opposite, and μέρος, part or portion) are stereoisomers that are nonsuperimposable complete mirror images of each other, much as ones left and right hands are the same but opposite. ... For the Second Person album, see Chromatography (album). ...


While structural isomers typically have different chemical properties, stereoisomers behave identically in most chemical reactions, except in their reaction with other stereoisomers. Enzymes however can distinguish between different enantiomers of a compound, and organisms often prefer one isomer over the other. Some stereoisomers also differ in the way they rotate polarized light. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... This article treats polarization in electrodynamics. ...


Other types of isomerism exist outside this scope. Topological isomers called topoisomers are generally large molecules that wind about and form different shaped knots or loops. Molecules with topoisomers include catenanes and DNA. Topoisomerase enzymes can knot DNA and thus change its topology. There are also isotopomers or isotopic isomers that have the same numbers of each type of isotopic substitution but in chemically different positions. In nuclear physics, nuclear isomers are excited states of atomic nuclei. Topology (Greek topos = place and logos = word) is a branch of mathematics concerned with the study of topological spaces. ... Topoisomers or topological isomers are molecules with the same chemical formula but different topologies. ... Catenanes are interlocked macrocyclic rings. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Topoisomerase I solves the problem caused by tension generated by winding/unwinding of DNA. It wraps around DNA and makes a cut permitting the helix to spin. ... Isotopomers (isotopic isomers) are isomers having the same number of each isotopic atom but differing in their positions. ... The word isotopic has a number of different meanings, including: In the physical sciences, to do with chemical isotopes; In mathematics, to do with a relation called isotopism. ... Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... A nuclear isomer is a metastable or isomeric state of an atom caused by the excitation of a proton or neutron in its nucleus so that it requires a change in spin before it can release its extra energy. ...


History

Isomerism was first noticed in 1827, when Friedrich Woehler prepared cyanic acid and noted that although its elemental composition was identical to fulminic acid (prepared by Justus von Liebig the previous year), its properties were quite different. This finding challenged the prevailing chemical understanding of the time, which held that chemical compounds could be different only when they had different elemental compositions. After additional discoveries of the same sort were made, such as Woehler's 1828 discovery that urea had the same atomic composition as the chemically distinct ammonium cyanate, Jöns Jakob Berzelius introduced the term isomerism to describe the phenomenon. Friedrich Wöhler Friedrich Wöhler (July 31, 1800 - September 23, 1882) was a German chemist, best-known for his synthesis of urea, but also the first to isolate several of the elements. ... Cyanic acid is a colourless poisonous liquid with a boiling point of 23. ... Resonance forms of fulminic acid Fulminic acid was discovered in 1824 by Justus von Liebig. ... Freiherr Justus von Liebig (May 12, 1803 in Darmstadt, Germany – April 18, 1873 in Munich, Germany) was a German chemist who made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry. ... Look up chemical compound in Wiktionary, the free dictionary. ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Nonproprietary Names (rINN) in use in Europe. ... Friherre Jöns Jakob Berzelius (August 20, 1779 – August 7, 1848) was a Swedish chemist. ...


In 1849, Louis Pasteur separated tiny crystals of tartaric acid into their two mirror-image forms. The individual molecules of each were the left and right optical stereoisomers, solutions of which rotate the plane of polarized light in opposite directions. Louis Pasteur (December 27, 1822 – September 28, 1895) was a French chemist best known for his remarkable breakthroughs in microbiology. ... Tartaric acid is a white crystalline organic acid. ... A mirror image is a mirror based duplicate of a single image. ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... This article does not cite any references or sources. ...


See also


  Results from FactBites:
 
Testing the physics of nuclear isomers (961 words)
An isomer is a long-lived excited state of an atom's nucleus--a state in which decay back to the nuclear ground state is inhibited.
A nuclear isomer is an atom whose nucleus is in a higher energy state than its ground state.
The long lifetime results because transition to the ground state would require a large change either in the spatial structure of the atom's nucleus (for a shape isomer) or in the angular momentum (a measure of the spin of the nucleus) between the isomer and the nuclear ground state (for a spin isomer).
isomer. The Columbia Encyclopedia, Sixth Edition. 2001-05 (952 words)
Isomers are classified as structural isomers, which have the same number of atoms of each element and molecular weight but different bonding patterns (see chemical bond), or as stereoisomers, which have the same number of atoms of each element, molecular weight, and bonding pattern but in which the atoms have different spatial relationships.
Tautomers are structural isomers that readily convert from one isomeric form to another and therefore exist in equilibrium.
Position isomers have similar chemical properties since they differ only in the location of the functional group (e.g., the OH in an alcohol or the double bond in an alkene).
  More results at FactBites »

 
 

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