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Isomer
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Isomer
In chemistry, isomers are molecules or polyatomic ions with an identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers.
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ.
Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest.
The English word "isomer" (/ˈaɪsəmər/) is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish isomerisk; which in turn was coined from Greek ἰσόμερoς isómeros, with roots isos = "equal", méros = "part".
Structural isomers have the same number of atoms of each element (hence the same molecular formula), but the atoms are connected in distinct ways.
For example, there are three distinct compounds with the molecular formula :
![{\displaystyle {\mathrm {C} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{8}}\mathrm {O} }}](https://wikimedia.org/api/rest_v1/media/math/render/svg/8c41f8d557f0a16aa1dd809d618dbbe7cf1729c1)
The first two isomers shown of are propanols, that is, alcohols derived from propane. Both have a chain of three carbon atoms connected by single bonds, with the remaining carbon valences being filled by seven hydrogen atoms and by a hydroxyl group comprising the oxygen atom bound to a hydrogen atom. These two isomers differ on which carbon the hydroxyl is bound to: either to an extremity of the carbon chain propan-1-ol (1-propanol, n-propyl alcohol, n-propanol; I) or to the middle carbon propan-2-ol (2-propanol, isopropyl alcohol, isopropanol; II). These can be described by the condensed structural formulas and .
![{\displaystyle {\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {C} {-}\mathrm {CH} {\vphantom {A}}_{\smash[{t}]{2}}{-}\mathrm {CH} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {OH} }}](https://wikimedia.org/api/rest_v1/media/math/render/svg/6d4c1afb5919de9c5e518068570204cfefae7675)
![{\displaystyle {\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {C} {-}\mathrm {CH} (\mathrm {OH} ){-}\mathrm {CH} {\vphantom {A}}_{\smash[{t}]{3}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e6d4babdd48d017f53a22e9db02c770baedd7f1d)
The third isomer of is the ether methoxyethane (ethyl-methyl-ether; III). Unlike the other two, it has the oxygen atom connected to two carbons, and all eight hydrogens bonded directly to carbons. It can be described by the condensed formula .
![{\displaystyle {\mathrm {H} {\vphantom {A}}_{\smash[{t}]{3}}\mathrm {C} {-}\mathrm {CH} {\vphantom {A}}_{\smash[{t}]{2}}{-}\mathrm {O} {-}\mathrm {CH} {\vphantom {A}}_{\smash[{t}]{3}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e22802c7812dc66a3f2429a9c666294d15ad9a41)
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Isomer
In chemistry, isomers are molecules or polyatomic ions with an identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers.
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ.
Isomeric relationships form a hierarchy. Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues. The depth of analysis depends on the field of study or the chemical and physical properties of interest.
The English word "isomer" (/ˈaɪsəmər/) is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish isomerisk; which in turn was coined from Greek ἰσόμερoς isómeros, with roots isos = "equal", méros = "part".
Structural isomers have the same number of atoms of each element (hence the same molecular formula), but the atoms are connected in distinct ways.
For example, there are three distinct compounds with the molecular formula :
The first two isomers shown of are propanols, that is, alcohols derived from propane. Both have a chain of three carbon atoms connected by single bonds, with the remaining carbon valences being filled by seven hydrogen atoms and by a hydroxyl group comprising the oxygen atom bound to a hydrogen atom. These two isomers differ on which carbon the hydroxyl is bound to: either to an extremity of the carbon chain propan-1-ol (1-propanol, n-propyl alcohol, n-propanol; I) or to the middle carbon propan-2-ol (2-propanol, isopropyl alcohol, isopropanol; II). These can be described by the condensed structural formulas and .
The third isomer of is the ether methoxyethane (ethyl-methyl-ether; III). Unlike the other two, it has the oxygen atom connected to two carbons, and all eight hydrogens bonded directly to carbons. It can be described by the condensed formula .
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