190
6 Construction of the Names of Complex Compounds
Priority sequence of ligands according to the CIP rules 2.
1. Higher > lower atomic number
2. Higher > lower mass number
3. Z; cis > E; trans
4. R,R; S,S > R,S; S,R. r > s
5. R,M
> S,P
For most of the practically important cases the first three criteria are sufficient for assigning conclusive priorities.
To visualize the stereochemical relationships in tetrahedral molecules
the following graphical conventions have been established, among which
can be freely chosen according to personal gusto.
CI
CI
H
CI
CI H
/
',.,
1\
H-C
-
C
-
Br~:, F =
\"F
Br .... ~F
Br+F -
F+Br
Br
H
H
CI
(Fischer- Projections)
(R)-Bromochlorofluoromethane (Br > CI > F > H)
Et
I
:P~"Me
H
HO > CHO > CH20H > H
D-Glyceraldehyde
(R)-2,3-Dihydroxypropanal
L-Cysteine
(R)-2-Amino-3-sulfanylpropanoic acid
(R) -Ethylmethylpropylphosphonium
(R)-Ethylmethylphosphane (H > :)
2 First comprehensive publication: R.S. Cahn, C,K. Ingold, V. Prelog, Angew. Chern. 1966,
78,413. Substantially modified and expanded version: V. Prelog, G. Helmchen, Angew.
Chern. 1982, 94, 614; Intern. Edition, 1982,21,567.