RULE-2 NUMBERING THE PARRENT CHAIN AND GIVE ALK NAME (ROOT WORD )
WORD ROOT ( ALK NAME ) learn this
C1   meth-
C2 ehth-
C3 prop-
C4 bute-
C5 pent-
C6 hex-
C7 hept-
C8 oct-
C9 non-
C10 dec-
C11 undec-
C12 dodec-
RULE- LOWEST NO. RULE
1. Pincipal funtional group gets lowest number then Branch if present
2. Sum of no. of side chain is lowest means no. start with nearest side chain or funtional group
3. Must include if present in parrent chain, nearest from in preference FC > double bone > triple bond > side chain ( -R )  in alphabetically
4. Select the principal funtional group (FC) from preference series
 -COOH > SO3H > COOR >COX > CONH2 >CN >NC > CHO > C=O> OH > SH > NH2 > OR > = > Triple bond > NO2 > X > R
5. If branch is long we do numbering and named it in brackets and arrange as substituent, for the branch start numbering at carbon attaches to parrent carbon.