The new method of rapid determination of chiral molecule

The New Method of Rapid Determination of Chiral Molecule Configuration The Triangle Method Han Yongsheng and Wang Callan Henan Normal University, P.R.China The methods of determining the configuration of a chiral molecule have been reported successively, such a s the hand-model nomenclature (1)and the "f 1,2,5"rule (2). This paper describes a new methodfor applying the CahnIngold-Prelog rules to determine the configuration of a chiral molecule directly from its Fischer projection formula. The compound R-Lm (a > b > c > d) containing one chiral atom i s taken a s a n example for illustrating the method. This method includes the following two steps:

(d) left ciockS-

wnfiguration wise

+a-

+a-

+. 4.-+. b

(d) right clock-

%iguration S-

+

(1)Connect the first three groups (a, b, c) to a triangle. (2) Determinate configuration:

A: If the smallest gmup (dl on the upper or lower side of the proiection formula and the sequence of a +b +cis clockwise, it is R configuration;if anticlockwise, it is S configuration. This is called the rule of 'upper and lower, clockwise, R". (See Figure 1.)

+.-

$.a a

C+b

(d) upper dockconfigurationR-

b-&

a

-

a a

a

(d) lower clockwise rationR a f i g u -

-C

C

C

C

Figure 2. Diagram showing application of Rule B

CH,+ c

COOH b

H d

i -+ ,,

c

-c

d

+b

d

(d) lower clockwise Rwnfiguration

d

or treat the original formula directly: Figure 1. Diagram showing application of Rule A.

cH3T a

B: if the smallest p u p (dl is on the left or right side of the projection formula and the sequence of a+b +cis clockwise, the configuration is S; if antidoekwise, the configuration is R. This is called the rule of" left and right, clockwise, S".(See Figure 2.)

-

-

COOH

C

I4

b

A ~ r a c t i c ael x a m ~ l eis eiven in Fienre 3. I n summaw. ". on

the basis of Fischer projection formulas, only remembering the rule that " u m e r and lower. clockwise. R: let? and rieht. clockwise, S", i6e chiral mol'ecnle co&g&ation c a n be determinated rapidly and aecrately without models or calculation.

Figure 3. Apractical application of the triangle method. Literature Cited 1. Garrett J.M. J. Chem. Edw. 11118.55.493

2.Dietzel.R.D.J. Cham.Educ 1970.56.451.

Volume 69 Number 4 April 1992

273