R-S notational system
R-S systemRULES OF PRIORITY ORDER:-
(1)According to the atomic number when only atom is present and in a group the
direct attached atom is considered with atomic number.
(2)When two or more groups have similar first atom, the priority is determined
by considering the atomic number of second atom.
(3)If the first atom of two same groups have same substitutes of higher no will
get more priority.
(4)More atomic number containing atom and how many atoms are present of the
higher atomic number containing elements.41.2 E-Z notation
The R-/S- notation is valid only for the the absolute configuration of a center having single
bonds only. In the case of a double bond, the traditionalcis/transnomenclature system is
not sufficiently accurate and theE-/Z-is currently preferred.
The basis is again the CIP priority rules.
See main discussion: E-Z notation^1
1 Chapter52.1on page 193