Chiral molecules Fischer projection formulas

Chiral, definition of, 260 Chiral axis. See Stereogenic axis Chiral center. See Stereogenic center Chiral drugs, 273 Chiral molecules, 259—263, 290 absolute configuration, 267, 292 Fischer projection formulas, 271-272, 278, 280, 292-293... 

Fischer projection formulas a-amino acids, 1056, 1103 carbohydrates, 973-974, 977, 1007 chiral molecules, 271—272, 292 two stereogenic centers, 276—278, 280, 293... 

Chemists, however, sometimes use formulas called Fischer projections to show three dimensions in chiral molecules such as acyclic carbohydrates. Fischer projection formulas are useful in cases where there are chirality centers at several adjacent carbon atoms, as is often the case in carbohydrates. Use of Fischer projection formulas requires rigjd adherence to certain conventions, however. Used carelessly, these projection formulas can easily lead to incorrect conclusions. 

Fischer projection (Sections 5.13 and 22.2C) A two-dimensional formula for representing the configuration of a chiral molecule. By convention, Fischer projection formulas are written with the main carbon chain extending from top to bottom with all groups eclipsed. Vertical lines represent bonds that project behind the plane of the page (or that lie in it). Horizontal lines represent bonds that project out of the plane of the page. 

Fischer projections provide a fnrther approach to the two-dimensional representations of three-dimensional formulae. They become particularly useful for molecules that contain several chiral centres, and are most frequently encountered in discussions of sugars (see... 

The Cahn-Ingold-Prelog rules (1956) are used to designate the configuration of each chiral C in a molecule in terms of the symbols R and S. These symbols come from the Latin, R from rectus (right) and S from sinister (left). Once told that the configuration of a chiral C is R or S, a chemist can write the correct projection or Fischer structural formulas. In our statement of the three rules the numerals 1, 2, 3, and 4 are used some chemists use letters a, b, c. and d in their place. 

Instead of using dashed and solid wedges to show the three-dimensional arrangements of groups in a chiral molecule, it is sometimes convenient to have a two-dimensional way of doing so. A useful way to do this was devised many years ago by Emil Fischer the formulas are called Fischer projections. 

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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