Tetrahedral chirality centers

There are two possible stereochemical courses for a ligand substitution reaction at a tetrahedral chiral center, inversion or retention of configuration. The terms inversion and retention apply only to the outcome of individual reactions, and are not used in reference to the outcome of a stereochemical cycle. The letters R (retention) or I (inversion) can be placed over reaction... 

Reactions That Generate Tetrahedral Chirality Centers 471... 

REACTIONS THAT GENERATE TETRAHEDRAL CHIRALITY CENTERS... 

When achiral molecules react to produce a compound with a single tetrahedral chirality center, the product will be a racemic form. 

This experiment, first done by Emil Fischer, estabhshed that D-glucose and D-mannose have the same configurations about C3, C4, and C5. Diastereomeric aldoses that differ in configuration at only one carbon (such as D-glucose and D-mannose) are called epimers. In general, any pair of diastereomers that differ in configuration at only a single tetrahedral chirality center can be called epimers. 

Part of the difficulty in assigning an absolute structure to cholesterol is that cholesterol contains eight tetrahedral chirality centers. This feature means that 2, or 256, possible stereoisomeric forms of the basic structure are possible, only one of which is cholesterol ... 

Eplmers, eplmerization (Sections 18.3A and 22.8) Diastereo-mers that differ in configuration at only a single tetrahedral chirality center. Epimerization is the interconversion of epimers. 

Molecules of 6,6 -dinitrobiphenyl-2,2 -dicarboxylic acid have no tetrahedral chiral center, and yet they can be resolved to a pair of enantiomers. Account for this chirality. 

Although cysteine has the same absolute configuration, it is an (R)-amino acid because of the manner in which priorities are assigned about its tetrahedral chiral center. 

Absolute Configuration The actual configuration of groups about a tetrahedral chiral center absolute configuration is specified by the R,S system. 

R,S-System (Section 5.7) A method for designating the configuration of tetrahedral chirality centers. 

Not all molecular chirality is a result of a tetrahedral chirality center, such as CHXYZ. Cumulated dienes (1,2-dienes, or allenes) are capable of generating molecular chirality. Identify, using models, which of the following cumulated dienes are chiral. 

Solution 2 Interchange of any two substituents converts the configuration of a tetrahedral chirality center to that of its enantiomer. There are only two possible configurations. If the models are not identical, they will have a mirror-image relationship. 

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