Absolutely "Simple" Configuration in Fischer Projection Formula K. R. N. Reddy University of Roorkee, Roorkee-247 667, India One can easilv assien the absolute confirmration at a particular chiral center Fischer projection Formula wheithe lowest prioritv substituent is present on either end of the verticailine (Fig. 1 J. When thelowest priority suhstituent is present on vertical in a Fischer proiection, then the clockthe configuration R &se direction of arrow 1 2 3 and anticlockwise gives S.However, a problem arises especially for a beginner when the lowest priority substituent is on either end of the horizontal line. Here I resent a table from which one can easilv assien the absolute configuration after designating priorities of the subwtituentn directlv honded to the chiral center. The method requires no rotation of substitueuts so as to bring the lowest priority one on to vertical line, thereby avoiding any
--
-
2
CHO
I
*OH$-C-OH
A
H
-
confusion for a learner. For glyceraldehyde (Fig. 2) where the lowest priority substituent is on a horizontal line the configuration is R according to the table. Similarly, for tartaric acid (Fig. 3), in which there are two chiral centers, we can assign the configuration by making use of the table. This method can be cross-checked by using other methods. One can see that this technique works for a large number of simple molecules where there are one or more chiral centers. General References
Mattem, D.L. J. C k m . E d w . 1985.62,191
4
I
H-C-OH
I
3
I
HO-C-H
*OH$-C-OH
I CHO
4
Flgve 1. (S) and (RiGlyceraldehydes.
2
2 Figure 3.2(R), 3(R~Tarlarlcacid
SlmDle Aimroach To Determine Conllauratton CHO
2
I
S NO.
H-C-OH !H20H
&+,l 3
Figure 2. (Wceraldehyde (according to table)
480
Journal of Chemical Education
1
2 3 4
Loureslpriority subsliituent on Vettical line Vettical line Horizomal line H~rlzondaIline
Directionafarmw CIockwise Anti~lo~k~ise Clockwise Anticlockwise
Conflgurallon
R S S R
