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In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. [1] Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and ...
The meso compound must not be confused with a 50:50 racemic mixture of the two optically-active compounds, although neither will rotate light in a polarimeter. It is a requirement for two of the stereocenters in a meso compound to have at least two substituents in common (although having this characteristic does not necessarily mean that the ...
The second step, once the diastereomers have formed, is to separate them using recrystallisation. This is possible because enantiomers have shared physical properties such as melting point and boiling point , but diastereomers have different chemical properties, so they can be separated like any two different molecules.
These include meso compounds, cis–trans isomers, E-Z isomers, and non-enantiomeric optical isomers. Diastereomers seldom have the same physical properties. In the example shown below, the meso form of tartaric acid forms a diastereomeric pair with both levo- and dextro-tartaric acids, which form an enantiomeric pair.
Enantioselective synthesis, also called asymmetric synthesis, [1] is a form of chemical synthesis.It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecule and which produces the stereoisomeric (enantiomeric or diastereomeric) products in unequal amounts."
2,3-Butanediamines can be prepared by hydrolyzing 2-ethoxy-4,5-dihydro-4,5-dimethylimidazole with barium hydroxide. [4] Alternative, it is produced by reduction of dimethylglyoxime with lithium aluminium hydride. [5] The meso and the d,l diastereomers can be separated by fractional crystallization of the hydrochlorides.
The Cram's rule of asymmetric induction named after Donald J. Cram states In certain non-catalytic reactions that diastereomer will predominate, which could be formed by the approach of the entering group from the least hindered side when the rotational conformation of the C-C bond is such that the double bond is flanked by the two least bulky groups attached to the adjacent asymmetric center. [3]
Diastereomers are distinct molecular configurations that are a broader category. [3] They usually differ in physical characteristics as well as chemical properties. If two molecules with more than one chiral centre differ in one or more (but not all) centres, they are diastereomers. All stereoisomers that are not enantiomers are diastereomers.