Tetrahedral stereogenic center

Fischer projection formulas can be used to represent molecules with several stereogenic centers and are commonly used for caibohydrates. For other types of structures, a more common practice is to draw the molecule in an extended conformation witii the main chain horizontal. In this arrangement, each tetrahedral caibon has two additional substituents, one facing out and one in. The orientation is specified widi solid wedged bonds for substituents facing out and with dashed bonds for substituents that point in. 

A tetrahedral atom with four different groups attached to it is a stereocenter (chiral center, stereogenic center)... 

CHBrClF contains a carbon atom bonded to four different groups. A carbon atom bonded to four different groups is called a tetrahedral stereogenic center. Most chiral molecules contain one or more stereogenic centers. 

With one tetrahedral stereogenic center, a molecule is always chiral. CHBrClF is a chiral molecule containing one stereogenic center. 

A necessary skill in the study of stereochemistry is the ability to locate and draw tetrahedral stereogenic centers. 

Always omit fixjm consideration all C atoms that can t be tetrahedral stereogenic centers. These include ... 

Any molecule with one tetrahedral stereogenic center is a chiral compound and exists as a pair of enantiomers. 

We have now seen many examples of compounds containing one tetrahedral stereogenic center. The situation is more complex for compounds with two stereogenic centers, because more stereoisomers are possible. Moreover, a molecule with two stereogenic centers may or may not be chiral. 

A meso compound is an achiral compound that contains tetrahedral stereogenic centers. 

Identical compounds have the same R,S designations at every tetrahedral stereogenic center. 

Locate all the tetrahedral stereogenic centers in discodermolide, a natural product isolated from the Caribbean marine sponge Discodermia dissoluta. Discodermolide is a potent tumor inhibitor, and shows promise as a drug for treating colon, ovarian, and breast cancers. 

Although the E2 reaction does not produce products with tetrahedral stereogenic centers, its transition state consists of four atoms that react at the same time, and they react only if they possess a particular stereochemical arrangement. 

Bongkrekic acid is a toxic compound produced by Pseudomonas cocovenenans, and isolated from a mold that grows on bongkrek, a fermented Indonesian coconut dish, (a) Label each double bond in bongkrekic acid as E or Z. (b) Label each tetrahedral stereogenic center as R or S. (c) How many stereoisomers are possible for bongkrekic acid ... 

How many tetrahedral stereogenic centers does PGF20 contain Draw its enantiomer. How many of its double bonds can exhibit cis-trans isomerism Considering both its double bonds and its tetrahedral stereogenic centers, how many stereoisomers are possible for PGF2a ... 

The stereochemistiy of carbonyl reduction follows the same principles we have previously learned. Reduction converts a planar sp hybridized carbonyl carbon to a tetrahedral sp hybridized carbon. What happens when a new stereogenic center is formed in this process With an achiral reagent like NaBITt or LiAlHi. a racemic product is obtained. For example, NaBH4 in CH3OH solution reduces 2-butanone, an achiral ketone, to 2-butanol, an alcohol that contains a new stereogenic center. Both enantiomers of 2-butanol are formed in equal amounts. 

Like reduction, addition of organometallic reagents converts an sp hybridized carbonyl carbon to a tetrahedral sp hybridized carbon. Addition of R - M always occurs from both sides of the trigonal planar carbonyl group. When a nevr stereogenic center is formed from an achiral starting material, an equal mixture of enantiomers results, as shown in Sample Problem 20.1. 

In 1891, only 10 years after the tetrahedral structure of carbon was proposed, Fischer determined the relative configuration of the four stereogenic centers in naturally occurring (-t)-glucose. This body of work is called the Fischer proof of the structure of glucose. 

BINAP is one of a small number of molecules that is chiral even though it has no tetrahedral stereogenic centers. Its shape makes it a chiral molecule. The two naphthalene rings of the BINAP molecule are oriented at almost 90° to each other to minimize steric interactions between the hydrogen atoms on adjacent rings. This rigid three-dimensional shape makes BINAP non-superimposable on its mirror image, and thus it is a chiral compound. 

Draw all possible constitutional isomers of a triacylglycerol formed from one mole each of palmitic, oleic, and linoleic acids. Locate the tetrahedral stereogenic centers in each constitutional isomer. 

Meso compound (Section 5.8) An achiral compound that contains two or more tetrahedral stereogenic centers. 

Stereogenic center (Section 5.3) A site in a molecule at which the interchange of two groups forms a stereoisomer. A carbon bonded to four different groups is a tetrahedral stereogenic center. A tetrahedral stereogenic center is also called a chirality center, a chiral center, or an asymmetric center. 

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