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In stereochemistry, an epimer is one of a pair of diastereomers. [1] The two epimers have opposite configuration at only one stereogenic center out of at least two. [2] All other stereogenic centers in the molecules are the same in each. Epimerization is the interconversion of one epimer to the other epimer.
There are many more pairs of diastereomers, because each of these configurations is a diastereomer with respect to every other configuration excluding its own enantiomer (for example, R,R,R is a diastereomer of R,R,S; R,S,R; and R,S,S). For n = 4, there are sixteen stereoisomers, or
Traditionally, double bond stereochemistry was described as either cis (Latin, on this side) or trans (Latin, across), in reference to the relative position of substituents on either side of a double bond. 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]
A racemic mixture is denoted by the prefix (±)-or dl-(for sugars the prefix dl-may be used), indicating an equal (1:1) mixture of dextro and levo isomers. Also the prefix rac- (or racem- ) or the symbols RS and SR (all in italic letters) are used.
Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. [1] The study of stereochemistry focuses on the relationships between stereoisomers, which are defined as having the same molecular formula and sequence of bonded atoms (constitution) but differing in the geometric positioning of the atoms in space.
For example, tartaric acid can exist as any of three stereoisomers depicted below in a Fischer projection. Of the four colored pictures at the top of the diagram , the first two represent the meso compound (the 2 R ,3 S and 2 S ,3 R isomers are equivalent), followed by the optically active pair of levotartaric acid (L-( R,R )-(+)-tartaric acid ...
Enantiotopic groups are identical and indistinguishable except in chiral environments. For instance, the CH 2 hydrogens in ethanol (CH 3 CH 2 OH) are normally enantiotopic, but can be made different (diastereotopic) if combined with a chiral center, for instance by conversion to an ester of a chiral carboxylic acid such as lactic acid, or if coordinated to a chiral metal center, or if ...
For example, 3-methyl-1-pentene with a rectus assignment is formatted as (R)-3-methyl-1-pentene. [12] An example of a (s) descriptor: (1R,2s,3S)-1,2,3-trichlorocyclopentane. A practical method of determining whether an enantiomer is R or S is by using the right-hand rule: one wraps the molecule with the fingers in the direction 1 → 2 → 3.