Question
Discuss the rules for IUPAC nomenclature of compounds containing two or more functional groups.
Solution
Rule 1. When an organic compound contains two or more different functional groups, one of the functional groups is selected from the principal functional group and all other groups are treated as substituents (also called secondary functional groups). The order of preference for selecting the principal functional group is:
Carboxylic acids > Anhydrides > Esters > Acid chlorides > Acid amides > Nitriles > Aldehydes > Ketones > Alcohols > Amines > Ethers
Rule 2. The principal chain present in polyfunctional compounds must be numbered in such a way that the principal functional group gets the lowest possible number followed by a double bond, triple bond and the substituents.
Principal functional group > Double bond > Triple bond > Substituents.
Rule 3. The prefixes for the secondary functional groups and other substituents should be placed in alphabetical order. If the groups of the same preference occupy identical positions from either end of the parent chain, the lower number must be given to the group whose prefix comes first in the alphabetical order.
Rule 4. If an unbranched carbon chain is directly linked to more than two like functional groups, the organic compound is named as a derivative of the parent alkane which does not include the carbon atoms of the functional groups.
If however, all the three like groups are not directly linked to the unbranched carbon chain, the two like groups are included in the parent chain while the third which forms the side chain is considered as a substituent group. For example
Carboxylic acids > Anhydrides > Esters > Acid chlorides > Acid amides > Nitriles > Aldehydes > Ketones > Alcohols > Amines > Ethers
Rule 2. The principal chain present in polyfunctional compounds must be numbered in such a way that the principal functional group gets the lowest possible number followed by a double bond, triple bond and the substituents.
Principal functional group > Double bond > Triple bond > Substituents.
Rule 3. The prefixes for the secondary functional groups and other substituents should be placed in alphabetical order. If the groups of the same preference occupy identical positions from either end of the parent chain, the lower number must be given to the group whose prefix comes first in the alphabetical order.
Rule 4. If an unbranched carbon chain is directly linked to more than two like functional groups, the organic compound is named as a derivative of the parent alkane which does not include the carbon atoms of the functional groups.
If however, all the three like groups are not directly linked to the unbranched carbon chain, the two like groups are included in the parent chain while the third which forms the side chain is considered as a substituent group. For example
