Isomerism

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.

thumb|upright=1.3|alt=An amino acid, illustrated in two different ionization states. First, it has a neutral amine and neutral carboxylic acid. Second, it has a protonated ammonium cation and deprotonated carboxylate anion.| The tautomers of an amino acid: (1) neutral and (2) zwitterionic forms

distinct arrangements of substituents around double bonds in chemistry

thumb|(S)-(+)-lactic acid (left) and (R)-(–)-lactic acid (right) are non-superposable mirror images of each other.

Favipiravir, sold under the brand name Avigan among others, is an antiviral medication used to treat influenza in Japan. It is also being studied to treat a number of other viral infections, including SARS-CoV-2. Like the experimental antiviral drugs T-1105 and T-1106, it is a pyrazinecarboxamide derivative.

{| align="right" class="wikitable" |- !colspan="2"|Diastereomers that are also epimers |- |bgcolor="#FFFFFF"| 150px |bgcolor="#FFFFFF"| 150px |- |bgcolor="#FFFFFF"| 166px |bgcolor="#FFFFFF"| 144px |- | D-threose | D-erythrose |}

thumb|right|Two kinds of stereoisomers|200px

compound whose molecule has the same number of atoms of each element

right|300px|thumb|Atropisomers of 6,6'-dinitro-2,2'-diphenic acid were first experimentally described case, by Christie and Kenner (1922).

type of structural isomerism in which a polyatomic ligand or moiety can be connected via different atoms

molecule interconvertable with another through pericyclic reactions

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350 px|thumb|Isotopomers of isotopically modified ethanol. The molecule at the bottom left is not an isotopomer of any other depicted molecule. Isotopomers or isotopic isomers are isomers which differ by isotopic substitution, and which have the same number of atoms of each isotope but in a different arrangement. For example, CH3OD and CH2DOH are two isotopomers of monodeuterated methanol.

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hypothetical isomer of benzene

Measurements of stable atom orientations

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