Revised Cahn-Ingold-Prelog (CIP) Rules - 1982

The lower numbered rule precedes the higher.

Rule Description
0 Nearer end of axis or side of plane precedes farther. Applied to even numbered cumulenes (allenes) and biphenyls with restricted rotation.
1 Higher atomic number precedes lower. Br > Cl > O > N > C > H
2 Higher atomic mass precedes lower. D > H; 81Br > 79Br
3 Seqcis precedes Seqtrans. Z precedes E
4 Like pair R,R=lk or S,S=lk precedes unlike pair R,S=ul or S,R=ul; and M,M=lk or P,P=lk precedes M,P=ul or P,M=ul; and R,M=lk or S,P=lk precedes R,P=ul or S,M=ul; and M,R=lk and P,S=lk precedes M,S=ul or P,R=ul; also, r precedes s
5 R precedes S; and M precedes P

For the 2013 IUPAC CIP rules with illustrations, click here.