source: Khan academy
Rules:IUPAC of Aliphatic compounds containing one functional group-
i) Longest chain-
Selection of longest parent chain including functional group, even if it is not the actual longest continuous chain.
ii) Numbering of parent chain-
a) The numbering of parent carbon chain is carried out in such a way that carbon linked to functional group gets the lowest number even if alkyl groups are present because alkyl groups are placed very below in priority table.
b) When chain terminating group such as -CHO, -COOH, -COOR, -CONH2, -CN etc. is present as functional group, it must be assigned number one (1).
iii) The last ‘e’ of the primary suffix is dropped & secondary suffix representing the functional group is added . The number giving the position of functional group is written as –
iv) If two or more identical groups are present then di, tri, tetra etc. is added before the designation of functional group present.