Stereochemistry Fischer projection formulas

The relative configuration of adjacent substituents in a Fischer projection formula are designated erythro if they are on the same side and threo if they are on the opposite side. The stereochemistry of adjacent stereocenters can also be usefully represented... 

It was in connection with his studies on carbohydrate stereochemistry that Emil Fischer invented his system of projection formulas. Because we will be using these formulas here, it might be wise for you to review Sections 5.7 through 5.9. Recall that, in a Fischer projection formula, horizontal lines show groups that project above the plane of the paper toward the viewer vertical lines show groups that project below the plane of the paper away from the viewer. Thus, R-(-F)-glyceraldehyde can be represented as... 

The Fischer projection is a convenient way of showing the configurations of the linear forms of monosaccharides. This convention depicts the concepts of stereochemistry established by Jacobus Henricus van t Hoff and Joseph Achille Le Bel in a simplified form. While these abbreviated structural formulas are simple to write and easy to visualize, there are some guidelines that should be taken into account when converting a three-dimensional structure into a Fischer projection and in its manipulation (Fig. 1.2) ... 

How can we represent the stereochemistry of the cyclic forms of sugars One approach uses Fischer projections. We simply draw elongated lines to indicate the bonds formed npon cyclization, preserving the basic grid of the original formula. Be careful not to confnse the three new apices of the ensning rectangle with carbon atoms. 

Natural products of the general formula PhCH(OH)CH(NHMe)CH3 are isolated from Ephedra species and are called ephedrine and pseudoephedrine. They have various physiological effects, including uses as decongestants and appetite suppressants. Draw all four of the possible stereoisomers as Fischer projections, and assign the stereochemistry at each chiral center. Why do ephedrine and pseudoephedrine have different physiological effects Do the natural and unnatural isomers have different effects What is the relationship of these molecules to methamphetamine ... 

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