In chemistry two stereoisomers are said to be enantiomers if one can be superimposed on the mirror image of the other. Enantiomers are mirror images of one another much as a right hand is the mirror image of a left hand. Chemistry (in Greek: χημεία) is the science of matter and its interactions with energy and itself (see physics, biology). ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ...
Enantiomers rotate planepolarized light by equal amounts but in opposite directions. A solution of equal parts of an optically active isomer and its enantiomer is known as a racemic solution and has a net rotation of plane polarized light of zero. A more in-depth explanation of this is in the footnotes for optical isomerism. In mathematics, a plane is the fundamental two-dimensional object. ... This article treats polarization in electrodynamics. ... In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecules. ... Optical isomerism is a form of isomerism (specifically stereoisomerism) whereby the different 2 isomers are the same in every way except being non-superimposable mirror images1 of each other. ...
Enantiomers will have the opposite prefixes of each other:
D- becomes L-
dextro becomes levo
(+)- becomes (-)-
R- becomes S-
Stereo chemistry of enantiomers is of great importance nowadays. Food and Drug Administration (FDA) of the United States of America, recently recommended that drug molecules having stereocentres should be given to the patients only in the active enantiomeric form and not as a racemic mixture.
Definitions:
Any non-racemic chiral substance is called scalemic
A chiral substance is enantiopure or homochiral when only one of two possible enantiomers is present.
A chiral substance is enantioenriched or heterochiral when an excess of one enantiomer is present but not to the exclusion of the other.
enantiomeric excess or ee is a measure for how much of one enantiomer is present compared to the other. For example in a sample with 40% ee in R, the remaining 60% is racemic with 30% of R and 30% of S so that the total amount of R is 70%.
External link
Course notes (http://www.chem.umd.edu/courses/chem233mazz/chapternotes/chapter9notes.pdf) for a lecturer's introduction to stereochemistry and enantiomers.
infelicitous stereochemical nomenclatures (http://www.uottawa.ca/publications/interscientia/inter.4/eliel/eliel.html) for stereochemical nomenclature
An alternative to using an enantioselective hydrocyanation catalyst to prepare chiral cyanohydrins is enantioselective dehydrocyanation, that is, the use of an enantioselective catalyst to effect the enrichment of a mixture of chiral cyanohydrins by preferentially converting one enantiomer in the mixture into hydrogen cyanide and the corresponding aldehyde or ketone.
A convenient method of expressing enantiomeric enrichment uses the concept of enantiomericexcess ("ee"), expressed by ##EQU2## wherein E1 is the amount of the first chiral form of the cyanohydrin and E2 is amount of the second chiral form of the same cyanohydrin.
Enantiomeric enrichment of such immiscible enantiomeric mixtures of cyanohydrins is especially effective when the solubility of the aldehyde reaction product in the catalyst-containing solvent is low and is lower than the solubility of the mixture of cyanohydrins in the catalyst-containing solvent.
We developed a method of kinetic resolution and electrospray ionization mass spectrometry that can be used to determine enantiomeric composition of alcohols and amines to within ±10% enantiomericexcess.
Enantiomericexcess of a series of samples can be measured as rapidly as 2 minutes per sample, with as little as 10 nmol of material.
1) and used the technique to measure the enantiomeric composition of chiral epoxides and lactones, by reaction with mass-tagged amines.
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