Diastereomer

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Diastereomer

Erythro redirects here. For the fictional planet, see Erythro (Asimov)
Erythro (Asimov)

Erythro is the name of the moon of Megas, a gas giant in the science fiction novel Nemesis , written by Isaac Asimov. Erythro is part of a red dwarf star system passing close to the Solar System....
.

Diastereomers (or diastereoisomers) are stereoisomers that are not enantiomer
Enantiomer

In chemistry, an enantiomer is one of two stereoisomers that are Superpose complete mirror images of each other, much as one's left and right Chirality are "the same" but opposite....
s (non-superposable mirror images of each other). Diastereomers can have different physical properties and different reactivity. In another definition diastereomers are pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other .

In simpler terms two stereoisomers are said to be diastereoisomers if they are not mirror images of each other and one or more stereogenic centers differ between the two stereoisomers.

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Erythro redirects here. For the fictional planet, see Erythro (Asimov)
Erythro (Asimov)

Erythro is the name of the moon of Megas, a gas giant in the science fiction novel Nemesis , written by Isaac Asimov. Erythro is part of a red dwarf star system passing close to the Solar System....
.
Diastereomers (or diastereoisomers) are stereoisomers that are not enantiomer
Enantiomer

In chemistry, an enantiomer is one of two stereoisomers that are Superpose complete mirror images of each other, much as one's left and right Chirality are "the same" but opposite....
s (non-superposable mirror images of each other). Diastereomers can have different physical properties and different reactivity. In another definition diastereomers are pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other .

In simpler terms two stereoisomers are said to be diastereoisomers if they are not mirror images of each other and one or more stereogenic centers differ between the two stereoisomers. According to this same definition, cis-trans isomerism is a form of diastereomerism.

If a molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
contains a single asymmetric carbon
Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
or stereocenter
Stereocenter

A stereocenter, or stereogenic center, is any point, though not necessarily an atom, in a molecule bearing groups such that an interchanging of any two groups leads to a stereoisomer ....
, it will form two mirror images. If a molecule contains two asymmetric carbons, there are up to 4 possible configurations, and they cannot all be mirror images of each other. The possibilities continue to multiply as there are more asymmetric centers in a molecule. In general, the number of diastereomers of a molecule can be determined by calculating 2n, where n=the number of chiral centers in the molecule. This holds true except in cases where the molecule has meso
Meso

Meso may refer to:*...
forms.

Tartaric acid
Tartaric acid

Tartaric acid is a white crystalline organic acid. It occurs naturally in many plants, particularly grapes, bananas, and tamarinds, and is one of the main acids found in wine....
contains two asymmetric centers, but two of the "isomers" are equivalent and together are called a meso compound
Meso compound

A meso compound or meso isomer is an non-optically active member of a set of stereoisomers, at least two of which are optically active. This means that despite containing two or more stereocenters it is not Optical isomerism....
. This configuration is not optically active, while the remaining two isomers are D- and L- mirror images, i.e., enantiomers. The meso form is a diastereomer of the other forms.

(natural) tartaric acid
L-(+)-tartaric acid
dextrotartaric acid D-(-)-tartaric acid
levotartaric acid
mesotartaric acid
(1:1)
DL-tartaric acid
"racemic acid"

The families of 4, 5 and 6 carbon carbohydrate
Carbohydrate

Carbohydrates or saccharides are the most abundant of the four major classes of biomolecules. They fill numerous roles in living things, such as the storage and transport of energy and structural components ....
s contain many diastereomers because of the large numbers of asymmetric centres in these molecules. Two common prefixes used to distinguish diastereomers are threo and erythro. When drawn in the Fischer projection
Fischer projection

The Fischer projection, devised by Hermann Emil Fischer in 1891, is a two-dimensional representation of a Three-dimensional space organic molecule by projection....
the erythro isomer has two identical substituents on the same side and the threo isomer has them on opposite sites. Cis-trans isomerism and conformational isomerism
Conformational isomerism

In chemistry, conformational isomerism is a form of stereoisomerism in which molecules with the same structural formula exist as different conformational isomers or conformers in 3-D due to rotations about one or more sigma bond....
are also forms of diastereomerism.

Diastereoselectivity is the preference for the formation of one or more than one diastereomer over the other in an organic reaction
Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and organic redox reaction....
.

Applications
As stated, two enantiomers will have identical physical properties, while diastereomers will not. This knowledge is harnessed in chiral synthesis
Chiral synthesis

Asymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is organic synthesis which introduces one or more new and desired elements of chirality....
to separate a mixture of enantiomers. This is the principle behind chiral resolution
Chiral resolution

Chiral resolution in stereochemistry is a process for the separation of racemic compounds into their enantiomers. It is an important tool in the production of optically active drugs....
. After preparing the diastereomers, they are separated by chromatography
Chromatography

Chromatography is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture dissolved in a "mobile phase" through a stationary phase, which separates the analyte to be measured from other molecules in the mixture and allows it to be isolated....
or recrystallization
Recrystallization

Recrystallization is a physical process that has meanings in chemistry, metallurgy and geology....
.