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Reactions at a single chiral carbon, leading to a chiral product (chiral -> chiral)
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  1. Stereochemistry - Wikipedia
  2. Stereochemistry
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From Wikipedia, the free encyclopedia. Archived from the original on Biochemical Pharmacology. Nature Chemistry. Bibcode : NatCh Modern Physical Organic Chemistry. University Science July 15, , pp. Chirality Racemic mixture. Concepts in organic chemistry. Basic reaction mechanisms. Electrophilic addition Nucleophilic addition Free-radical addition Cycloaddition.

Rate equation Rate-determining step.

Branches of chemistry. Glossary of chemical formulas List of biomolecules List of inorganic compounds Periodic table. Stereochemistry , Term originated c. Louis Pasteur had shown in that tartaric acid has optical activity and that this depends on molecular asymmetry, and Jacobus H.

Stereochemistry deals with stereoisomers and with asymmetric synthesis. John Cornforth b. Info Print Cite. Submit Feedback. To describe a mixture that falls in-between these two extremes, one can use the enantiomer excess ee relation.

Fischer Projections - Stereochemistry

This is used for when one enantiomer is in excess of the other enantiomer in a mixture. The enantiomer excess equation tells us how much of one enantiomer is in excess of a racemic solution since in a racemate the ratio of enantiomers is The enantiomer excess is also known as optical purity and can be found by the relation:. Find optical purity and actual enantiomer composition of the sample.

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Stereochemistry - Wikipedia

Thus, it can be concluded that the artifact under examination has an actual composition of If two enantiomers of a chiral molecule were isolated into two different containers in pure form, it would be extremely difficult to distinguish the two based on just their physical properties such as boiling points, melting points, and densities.

Because only certain enantiomers of certain drugs are effective while the other enantiomers are ineffective or even detrimental to the body, it is very important to be able to distinguish enantiomers. Fortunately chiral molecules possess a unique property that rotates the chiral molecules in a particular direction when a special kind of light called plane-polarized light is passed through a sample containing the enantiomers. This unique reaction that chiral molecules have with plane-polarized light is called optical activity which results in enantiomers often being referred to as optical isomers.

The direction of rotation of any particular chiral molecule will always be the same and the enantiomer of that chiral molecule will have an opposite direction of rotation. Plane-polarized light result from passing a beam of ordinary light through a special material called a polarizer. A polarizer serves as a filter for the light waves that pass through it and filters out all but one light wave, the plane-polarized light wave [2].

Once the light has been filtered to just the plane-polarized light, the light wave travels through the chiral molecules. The electric field of the light wave interacts with the electrons around the chiral molecule and causes the molecule to rotate at a particular direction; this rotation is called optical rotation [2]. If there is optical rotation in the sample, then the sample is referred to as optically active.

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To determine if a sample is optically active, optical rotations have to be measured with a polarimeter. Oftentimes reactions that yield chiral molecules are not stereospecific which may lead to products that have a mixture of enantiomers. This reaction mixture is referred to as a racemic mixture because when a plane-polarized light passes through this sample, half of the chiral molecules would be rotating clockwise while the other half would be rotating counterclockwise. This results in a sample with no net optical activity.

However, when the ratio of enantiomers is not , then there will be optical activity. One of the major goals of pharmaceutical companies is to perform reactions that yield optically pure products because this saves them very much time from the purification process of optically impure samples, not to mention money on the reactants used during production. Amino acids are building blocks of protein. The general structure of an amino acid has an sp3 hybridized carbon atom linked to four other substituents.

Three of the four substituents attached to the carbon of all amino acids are an amino group and a carboxylic acid group and a hydrogen atom.

Stereochemistry

R can represent one of the twenty different side chains the twenty different amino acids have. The stereochemistry of amino acids are represented with an L,D system. The L,D system is essentially the same as the R,S system for absolute configuration with the exception that the L,D system is for amino acids. For the L,D system, L is the equivalent of the S absolute configuration leaving D to be the equivalent of the R absolute configuration.

Stereochemistry

Amino acids exist dominantly in the L absolute confirmation. There is no conclusive evidence for the dominance of the L isomer over the D isomer at the moment. Many speculate that the L isomer became the dominant amino acid configuration due to chance rather than any physical or chemical property.


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There have been experiments done trying to elucidate the reason behind the dominance of the L isomer. In the experiments, a protein would be artificially synthesized with only amino acids with the D absolute configuration. The conclusion was that the proteins made of only D amino acids were equally as active as the proteins made of L amino acids with the only difference being that the proteins made of D amino acids had reactions that were the reverse of the proteins made of L amino acids.

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Diastereomers are any stereoisomers that are not enantiomers. Thus, diastereomers are not mirror images of each other. Because diastereomers are stereoisomers that aren't mirror images of each other, they can be distinguished by different physical and chemical properties.

Thus, it is possible to separate diastereomers by standard laboratory techniques. Diastereomers arise when stereoisomers of a molecule have different configurations at at least one of their stereocenters but not all, for they would then be enantiomers. Each stereocenter possesses two configurations, so the number of stereoiosmers is increased by a factor of two. There are 3 stereocenters in the molecule below. The atoms have been switched in the first and third carbon. This is an example of diastereomers. If the second carbons atoms were switched also, then these two molecules would be enantiomers.

Cis and trans prefixes are essentially absent when naming alkenes with an E,Z system being used instead. The E,Z system sets priorities for carbon substituents the same way as the R,S system with the difference being that the double-bond having no bearing on the priority, only the two substituents that are single-bonded to the carbon.

The atoms have been switched at the stereocenter in ONLY the third carbon on right. This is an example of epimers.