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There are three common naming conventions for specifying one of the two enantiomers (the absolute configuration) of a given chiral molecule: the R/S system is based on the geometry of the molecule; the (+)- and (−)- system (also written using the obsolete equivalents d- and l-) is based on its optical rotation properties; and the D/L system is based on the molecule's relationship to ...
Chiral molecules can differ in their chemical properties, but are identical in their physical properties, which can make distinguishing enantiomers challenging. Absolute configurations for a chiral molecule (in pure form) are most often obtained by X-ray crystallography , although with some important limitations.
Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism (or spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form a ...
Different enantiomers or diastereomers of a compound were formerly called optical isomers due to their different optical properties. [29] At one time, chirality was thought to be restricted to organic chemistry, but this misconception was overthrown by the resolution of a purely inorganic compound, a cobalt complex called hexol , by Alfred ...
In nature, only one enantiomer of most chiral biological compounds, such as amino acids (except glycine, which is achiral), is present. Enantiomers differ by the direction they rotate polarized light: the amount of a chiral compound's optical rotation in the (+) direction is equal to the amount of its enantiomer's rotation in the (–) direction.
In case of penicillamine, the (S-isomer is used in the treatment of primary chronic arthritis, whereas the (R)-isomer has no therapeutic effect, as well as being highly toxic. [30] In some cases, the less therapeutically active enantiomer can cause side effects. For example, (S-naproxen is an analgesic but the (R-isomer causes renal problems. [31]
There is no strict relationship between the R/S, the D/L, and (+)/(−) designations, although some correlations exist. For example, of the naturally occurring amino acids, all are L, and most are (S). For some molecules the (R)-enantiomer is the dextrorotary (+) enantiomer, and in other cases it is the levorotary (−) enantiomer. The ...
Like the d-isomer, l-glucose usually occurs as one of four cyclic structural isomers—α- and β-l-glucopyranose (the most common, with a six-atom ring), and α- and β-l-glucofuranose (with a five-atom ring). In water solution, these isomers interconvert in matters of hours, with the open-chain form as an intermediate stage.