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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 ]
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).
The use of Fischer projections in non-carbohydrates is discouraged, as such drawings are ambiguous and easily confused with other types of drawing. The main purpose of Fischer projections is to show the chirality of a molecule and to distinguish between a pair of enantiomers. Some notable uses include drawing sugars and depicting isomers. [1]
Several isomers exist with the formula H−(C=O)−(CH 2)−(CHOH) 3 −H, but in deoxyribose all the hydroxyl groups are on the same side in the Fischer projection.The term "2-deoxyribose" may refer to either of two enantiomers: the biologically important d-2-deoxyribose and to the rarely encountered mirror image l-2-deoxyribose.
Functional isomers are special kinds of structural isomers, where certain groups of atoms exhibit a special kind of behavior, such as an ether or an alcohol. Stereoisomers may have many similar physicochemical properties (melting point, boiling point) and at the same time very different biochemical activities.
Because electron donating groups are both ortho and para directors, separation of these isomers is a common problem in synthetic chemistry. Several methods exist in order to separate these isomers: Column chromatography will often separate these isomers, as the ortho is more polar than the para in general.
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This image is a derivative work of the following images: File:Cell_membrane_detailed_diagram_en.svg licensed with PD-user . 2009-02-23T18:08:26Z Bibi Saint-Pol 877x361 (487132 Bytes) {{Information |Description= {{en|The cell membrane, also called the plasma membrane or plasmalemma, is a semipermeable lipid bilayer common to all living cells.