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Isomer: Difference between revisions
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In chemistry, '''isomers''' are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical isomers, and others. There are two main forms of isomerism: structural isomerism and stereoisomerism (spatial isomerism). | In chemistry, '''isomers''' are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical isomers, and others. There are two main forms of isomerism: structural isomerism and stereoisomerism (spatial isomerism). | ||
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===Enantiomers=== | ===Enantiomers=== | ||
[[File:File_Chirality_with_hands.png|thumb|right|Two enantiomers of a generic amino acid that is chiral.]] | |||
An enantiomer is one of two stereoisomers that are mirror images of each other that are non-superimposable (not identical). The model used to convey the idea of isomers being non-superimposable is a person's hands. One's left and right hands are the same except for opposite orientation. Organic compounds that contain a chiral carbon usually have two non-superimposable structures. A chiral carbon is a carbon attached to four completely different functional groups. The enantiomers will have a "left-hand" and a "right-hand" molecule. This property is used in naming the isomers: the "right-hand" is given the prefix (R), and the "left-hand" is given the prefix (S). Enantiomers rotate in plane-polarized light, and this property is also used in naming the enantiomers as either clockwise (prefix of dextro- or +) or anti-clockwise (prefix of levo or -). | An enantiomer is one of two stereoisomers that are mirror images of each other that are non-superimposable (not identical). The model used to convey the idea of isomers being non-superimposable is a person's hands. One's left and right hands are the same except for opposite orientation. Organic compounds that contain a chiral carbon usually have two non-superimposable structures. A chiral carbon is a carbon attached to four completely different functional groups. The enantiomers will have a "left-hand" and a "right-hand" molecule. This property is used in naming the isomers: the "right-hand" is given the prefix (R), and the "left-hand" is given the prefix (S). Enantiomers rotate in plane-polarized light, and this property is also used in naming the enantiomers as either clockwise (prefix of dextro- or +) or anti-clockwise (prefix of levo or -). | ||
===Nomenclature=== | |||
Often, the <small>D</small>/<small>L</small> system (with small caps) and the <small>d</small>/<small>l</small> system (with lower-case) are confused. The result is that the levorotary <small>l</small>-ephedrine is wrongly named <small>L</small>-ephedrine and the dextrorotary <small>d</small>-pseudoephedrine (the diastereomer) wrongly <small>D</small>-pseudoephedrine. | |||
== Chirality == | == Chirality == | ||
A chiral molecule is a type of molecule that has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom, where the carbon is attached to four entirely different functional groups. | A chiral molecule is a type of molecule that has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom, where the carbon is attached to four entirely different functional groups. | ||
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One example of this is with the [[dissociative]] drug [[DXM]]. DXM, or dextromethorphan, is the isomer that rotates clockwise in plane-polarized light. It has antitussive (cough suppressant) and dissociative effects. Levomethorphan is the isomer that rotates anti-clockwise in plane-polarized light. This difference in rotation can radically alter the effects and character of the drug; for example, levomethorphan is an [[opioid]] painkiller. | One example of this is with the [[dissociative]] drug [[DXM]]. DXM, or dextromethorphan, is the isomer that rotates clockwise in plane-polarized light. It has antitussive (cough suppressant) and dissociative effects. Levomethorphan is the isomer that rotates anti-clockwise in plane-polarized light. This difference in rotation can radically alter the effects and character of the drug; for example, levomethorphan is an [[opioid]] painkiller. | ||
[[File:DXM_chirality.png|thumb| | [[File:DXM_chirality.png|thumb|right|Two different chiral forms of methorphan can give rise to radically different effects.]] | ||
== Racemic mixture == | |||
In chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. A racemic mixture is the most common forms chemicals (psychoactive or not) end up synthesized as. | In chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. A racemic mixture is the most common forms chemicals (psychoactive or not) end up synthesized as. | ||
A racemate is optically inactive, meaning that there is no net rotation of plane-polarized light. Although the two enantiomers rotate plane-polarized light in opposite directions, the rotations cancel because they are present in equal amounts. | A racemate is optically inactive, meaning that there is no net rotation of plane-polarized light. Although the two enantiomers rotate plane-polarized light in opposite directions, the rotations cancel because they are present in equal amounts. | ||
In contrast to the two pure enantiomers, which have identical physical properties except for the direction of rotation of plane-polarized light, a racemate sometimes has different properties from either of the pure enantiomers. Different melting points are most common, but different solubilities and boiling points are also possible.<ref>https://en.wikipedia.org/wiki/Racemic_mixture | Racemic mixture | In contrast to the two pure enantiomers, which have identical physical properties except for the direction of rotation of plane-polarized light, a racemate sometimes has different properties from either of the pure enantiomers. Different melting points are most common, but different solubilities and boiling points are also possible.<ref>https://en.wikipedia.org/wiki/Racemic_mixture | Racemic mixture (Wikipedia)</ref> | ||
Pharmaceuticals may be available as a racemate or as the pure enantiomer (enantiopure), which might have different potencies and effects. Because biological systems have many chiral asymmetries, pure enantiomers frequently have very different biological effects. Examples include glucose and [[methamphetamine]].<ref>https://en.wikipedia.org/wiki/Racemic_mixture | Racemic mixture | Pharmaceuticals may be available as a racemate or as the pure enantiomer (enantiopure), which might have different potencies and effects. Because biological systems have many chiral asymmetries, pure enantiomers frequently have very different biological effects. Examples include glucose and [[methamphetamine]].<ref>https://en.wikipedia.org/wiki/Racemic_mixture | Racemic mixture (Wikipedia)</ref> | ||
== Enantiopure == | |||
A sample with only a single enantiomer is an enantiomerically pure, enantiopure or homochiral compound. | A sample with only a single enantiomer is an enantiomerically pure, enantiopure or homochiral compound. | ||
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*[[Scientific information]] | *[[Scientific information]] | ||
*[[Psychoactive substance index]] | *[[Psychoactive substance index]] | ||
==External links== | |||
*[https://en.wikipedia.org/wiki/Isomer Isomer (Wikipedia)] | |||
==References== | ==References== | ||
{{reflist|2}} | {{reflist|2}} | ||
[[Category:Chemistry]] | |||
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