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In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. [1] Isomerism refers to the existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties.
In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. [1] Enolization is an example of isomerization, as is tautomerization. [2] When the isomerization occurs intramolecularly it may be called a rearrangement reaction.
One example is the pair [CrCl(H 2 O) 5]Cl 2 •H 2 O and [Cr(H 2 O) 6]Cl 3. [1] The former has one water of crystallization but the latter does not. Another example is the pair of titanium(III) chlorides, [Ti(H 2 O) 6]Cl 3 and [Ti(H 2 O) 4 Cl 2]Cl(H 2 O) 2. The former is violet and the latter, with two molecules of water of crystallization, is ...
For example, butanol H 3 C−(CH 2) 3 −OH, methyl propyl ether H 3 C−(CH 2) 2 −O−CH 3, and diethyl ether (H 3 CCH 2 −) 2 O have the same molecular formula C 4 H 10 O but are three distinct structural isomers. The concept applies also to polyatomic ions with the same total charge. A classical example is the cyanate ion O=C=N − and ...
A pair of valence tautomers with formula C 6 H 6 O are benzene oxide and oxepin. [9] [10] Other examples of this type of tautomerism can be found in bullvalene, and in open and closed forms of certain heterocycles, such as organic azides and tetrazoles, [11] or mesoionic münchnone and acylamino ketene.
One of the two meso isomers of 1,2,3,4-tetrafluorospiropentane, with S 4 symmetry. Since a meso isomer has a superposable mirror image, a compound with a total of n chiral centers cannot attain the theoretical maximum of 2 n stereoisomers if one of the stereoisomers is meso. [4] A meso isomer need not have a mirror plane.
The isomerization energy, for example, for converting from a stable cis isomer to the less stable trans isomer is greater than for the reverse reaction, explaining why in the absence of isomerases or an outside energy source such as ultraviolet radiation a given cis isomer tends to be present in greater amounts than the trans isomer.
Topoisomers or topological isomers are molecules with the same chemical formula and stereochemical bond connectivities but different topologies. Examples of molecules for which there exist topoisomers include DNA, which can form knots, and catenanes. Each topoisomer of a given DNA molecule possesses a different linking number associated with it.