Fischer projection method

FIGURE 7.10 Representations of (2/ ,3/ )-dihydroxybutanoic acid, (a) The staggered conformation is the most stable but is not properly arranged to show stereochemistry according to the Fischer projection method. (6) Rotation about the C-2—C-3 bond gives the eclipsed conformation, and projection of the eclipsed conformation onto the page gives (c) a correct Fischer projection. 

In addition to the different bond orders, there are several other types of bonds to handle stereochemistry (bold, dotted and wavy bonds). Stereocenters are displayed by showing the respective atom in reverse video. For molecules with many stereocenters (e.g. sugar chemistry), the Fischer Projection Method can be used for entering stereocenters. (Figures 6,7)... 

Fischer projection Method for representing stereochemical relationships. The four bonds to a tetrahedral carbon are represented by a cross. The horizontal bonds are understood to project toward the viewer and the vertical bonds away from the viewer. 

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... 

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

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. 

For a thorough understanding of stereochemistry, it is useful to examine molecular models (like those depicted in Fig. 4.1). However, this is not feasible when writing on paper or a blackboard. In 1891, Emil Fischer greatly served the interests of chemistry by inventing the Fischer projection, a method of representing tetrahedral carbon atoms on paper. By this convention, the model is held so that the two bonds in front of the paper are horizontal and those behind the paper are vertical. 

Now we can understand why we cannot draw a Fischer projection sideways. If we did, we would be inverting the stereocenter. To draw the enantiomer of a Fischer projection, do not turn the drawing sideways. Instead, you should use the second method we saw for drawing enantiomers (place the mirror on the side of the compound and draw the reflection). Recall that this was the method that we used for drawings where wedges and dashes were implied but not shown. Fischer projections are another example of drawings that fit this criterion ... 

Now, we need to draw the enantiomer. For Fischer projections, we use the method where we place a mirror on the side, and then we draw the reflection ... 

Fischer polypeptide synthesis org chem A synthesis of peptides in which a-amino acids or those peptides with a free amino group react with acid halides of a-haloacids, followed by amination with ammonia. fish-ar pal-e pep,tTd. sin tha sas ) Fischer projection orgchem) A method for representing the spatial arrangement of groups around chiral carbon atoms the four bonds to the chiral carbon are represented by a cross, with the assumption that the horizontal bonds project toward the viewer and the vertical bonds away from the viewer fish-ar pra.jek-shon) Fischer s salt See cobalt potassium nitrite. fish-3rz solt)... 

An early method to picture the three-dimensional properties of molecules was the use of Fischer projections. In Fisher projections, bonds are drawn either vertically or horizontally. Bonds which are vertical project into file space behind the plane of file paper (blackboard, computer screen). Bonds which are horizontal project into file space in front of file plane of the paper (blackboard, computer screen). 

In the course of investigations of aspartyl dipeptide esters, we had to draw their chemical structures in a unified formula. In an attempt to find a convenient method for predicting the sweettasting property of new peptides and, in particular, to elucidate more definite structure-taste relationships for aspartyl dipeptide esters, we previously applied the Fischer projection technique in drawing sweet molecules in a unified formula 04). 

In our discussion of d and l sugars, we briefly mentioned a method for shortening the chain of an aldose by removing the aldehyde carbon at the top of the Fischer projection. Such a reaction, removing one of the carbon atoms, is called a degradation. 

Fischer Projections Stereoisomerism in Cyclic Compounds Methods of Determining Absolute Configuration Asymmetric Synthesis... 

Since all carbohydrates have chiral carbon atoms, it was recognized long ago that a standard method of repreientation is needed to describe carbo hydrate steneochemtsSfy. The method most commonly used employ s Fischer projections for depicting chirality centers on a flat page. 

Fischer projection formula (Section 27.2A) A method for representing stereogenic centers with the stereogenic carbon at the intersection of vertical and horizontal lines. Fischer projections are also called cross formulas. 

Although more representative of the actual structure of a compound, stereochemical structures are often difficult to draw quickly. An alternative method of depicting structures with tetrahedral carbon centers relies on the use of Fischer projections. 

It is sometimes useful to be able to draw a schematic diagram of the stereochemistry around a chiral carbon, especially when a molecule contains more than one chiral centre. The German chemist Emil Fischer solved this problem and his method of representing chiral centres is now called a Fischer projection. 

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