Fischer projections chirality

In an infinite Fischer projection, chirality is not consistent with the presence of the following elements of reflective synunetry (41, 46, 254) d, mirror plane containing the chain axis m, an infinite number of mirror planes perpendicular to the chain axis and/or c, mirror glide plane containing the chain axis. For... 

S. Capozziello, A. Lattanzi, Algebraic structure of central molecular chirality starting from Fischer projections. Chirality 15, 466 -71 (2003)... 

Fischer projection A method of representing three-dimensional structures in two-dimensional drawings in which the chiral atom(s) lies in the plane of the paper. The two enantiomeric forms of glyceraldehyde are represented as... 

Lei s relurn fo bromochlorofluoromelhane as a simple example of a chiral mole cule The Iwo enanliomers of BrClFCH are shown as ball and slick models as wedge and dash drawings and as Fischer projections m Figure 7 6 Fischer projeclions are always generated Ihe same way Ihe molecule is oriented so lhal Ihe verlical bonds al Ihe chiralily center are directed away from you and Ihe horizonlal bonds poinl toward you A projeclion of Ihe bonds onto Ihe page is a cross The chiralily center lies al Ihe center of Ihe cross bul is nol explicilly shown... 

Switching the positions of two groups in a Fischer projection reverses the config ration of the chirality center... 

When using Fischer projections for this purpose however be sure to remember what three dimensional objects they stand for One should not for example test for superim position of the two chiral stereoisomers by a procedure that involves moving any part of a Fischer projection out of the plane of the paper in any step... 

Relative to each other both hydroxyl groups are on the same side m Fischer pro jections of the erythrose enantiomers The remaining two stereoisomers have hydroxyl groups on opposite sides m their Fischer projections They are diastereomers of d and L erythrose and are called d and l threose The d and l prefixes again specify the con figuration of the highest numbered chirality center d Threose and l threose are enan tiomers of each other... 

Aldoses exist almost exclusively as their cyclic hemiacetals very little of the open chain form is present at equilibrium To understand their structures and chemical reac tions we need to be able to translate Fischer projections of carbohydrates into their cyclic hemiacetal forms Consider first cyclic hemiacetal formation m d erythrose To visualize furanose nng formation more clearly redraw the Fischer projection m a form more suited to cyclization being careful to maintain the stereochemistry at each chirality center... 

Glycine is the simplest ammo acid and the only one m Table 27 1 that is achiral The a carbon atom is a chirality center m all the others Configurations m ammo acids are normally specified by the d l notational system All the chiral ammo acids obtained from proteins have the l configuration at their a carbon atom meaning that the amine group IS at the left when a Fischer projection is arranged so the carboxyl group is at the top... 

Next translate the Fischer projection of l serine to a three dimensional represen tation and orient it so that the lowest ranked substituent at the chirality center IS directed away from you... 

Erythro (Section 7 11) Term applied to the relative configura tion of two chirality centers within a molecule The erythro stereoisomer has like substituents on the same side of a Fischer projection... 

Fischer projection (Section 7 7) Method for representing stereochemical relationships The four bonds to a chirality... 

Let s return to bromochlorofluoromethane as a simple example of a chiral molecule. The two enantiomers of BrCIFCH are shown as ball-and-stick models, as wedge-and-dash drawings, and as Fischer projections in Figure 7.6. Fischer projections are always generated the same way the molecule is oriented so that the vertical bonds at the chirality center are directed away from you and the horizontal bonds point toward you. A projection of the bonds onto the page is a cross. The chirality center lies at the center of the cross but is not explicitly shown. 

To verify that the Fischer projection has the R configuration at its chirality center, rotate the three-dimensional r epresentation so that the lowest-ranked atom (H) points away from you. Be careful to maintain the proper stereochemical relationships during the operation. 

L-Amino acid (Section 27.2) A description of the stereochemistry at the a-carbon atom of a chiral amino acid. The Fischer projection of an a-amino acid has the amino group on the left when the carbon chain is vertical with the carboxyl group at the top. 

Because carbohydrates usually have numerous chirality centers, it was recognized long ago that a quick method for representing carbohydrate stereochemistry is needed. In 1891, Emil Fischer suggested a method based on the projection of a tetrahedral carbon atom onto a flat surface. These Fischer projections were soon adopted and are now a standard means of representing stereochemistry at chirality centers, particularly in carbohydrate chemistry. 

Because a given chiral molecule can be drawn in many different ways, it s often necessary to compare two projections to see if they represent the same or different enantiomers. To test for identity, Fischer projections can be moved around on the paper, but only two kinds of motions are allowed moving a Fischer projection in any other way inverts its meaning. 

R,S stereochemical designations (Section 9.5) can be assigned to the chirality center in a Fischer projection by following three steps, as shown in Worked Example 25.1. 

Carbohydrates with more than one chirality center are shown in. Fischer projections by stacking the centers on top of one another. By convention, the carbony] carbon is always placed either at or near the top. Glucose, for... 

Follow the steps in the text. (1) Assign priorities to the four substituents on the chiral carbon. (2) Manipulate the Fischer projection to place the group of lowest priority at the top by carrying out one of the allowed motions. (3) Determine the direction 1 —> 2 — 3 of the remaining three groups. 

Problem 25.4 Redraw the following molecule as a Fischer projection, and assign R or 5 configuration to the chirality center (yellow-green = Cl) ... 

Figure 25.2 Some naturally occurring D sugars. The -OF group at the chirality center farthest from the carbonyl group has the same configuration as

Fischer projections of the tour-, five-, and six-carbon d alcloses are shown in Figure 25.3. Starting with D-glyceraldehyde, we can imagine constructing the two d aldotetroses by inserting a new chirality center just below the aldehyde carbon. Each of the two d aldotetroses then leads to two d aldopentoses (four total), and... 

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