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Two older prefixes still commonly used to distinguish diastereomers are threo and erythro. In the case of saccharides, when drawn in the Fischer projection the erythro isomer has two identical substituents on the same side and the threo isomer has them on opposite sides. [ 7 ]
Erythrose is a tetrose saccharide with the chemical formula C 4 H 8 O 4.It has one aldehyde group, and is thus part of the aldose family. The natural isomer is D-erythrose; it is a diastereomer of D-threose.
The stereoisomers β-D-glucopyranose and β-D-mannopyranose are epimers because they differ only in the stereochemistry at the C-2 position.The hydroxy group in β-D-glucopyranose is equatorial (in the "plane" of the ring), while in β-D-mannopyranose the C-2 hydroxy group is axial (up from the "plane" of the ring).
Discounting isomers that are equivalent under rotations, there are nine isomers that differ by this criterion, and behave as different stable substances (two of them being enantiomers of each other). The most common one in nature ( myo -inositol) has the hydroxyls on carbons 1, 2, 3 and 5 on the same side of that plane, and can therefore be ...
Very often, cis–trans stereoisomers contain double bonds or ring structures. In both cases the rotation of bonds is restricted or prevented. [4] When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, whereas when the substituents are oriented in opposing directions, the diastereomer is referred to as trans.
Isomers themselves exist in many varieties but can generally be classified as structural isomers or stereoisomers. Structural isomers have a different ordering of bonds and/or different bond connectivity from one another, as in the case of hexane and its four other isomeric forms ( 2-methylpentane , 3-methylpentane , 2,2-dimethylbutane , and 2 ...
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A simple example of cis–trans isomerism is the 1,2-disubstituted ethenes, like the dichloroethene (C 2 H 2 Cl 2) isomers shown below. [7] Dichloroethene isomers. Molecule I is cis-1,2-dichloroethene and molecule II is trans-1,2-dichloroethene.