Principal functional group-Polyfunctional Organic Compounds

If the organic compound includes two or more functional groups, one of the functional sets is chosen as the principal functional group whereas all the remaining functional groups (as well called the secondary functional groups) are treated as substituents. The subsequent order of preference is used when selecting the principal functional group.

Sulphonic acids > carboxylic acids > anhydrides > esters > acid chlorides > acid amides > nitriles > aldehydes > ketones > thiols > alcohols >alkenes > alkynes.

All the remaining functional sets like halo (fluoro, chloro, bromo, iodo), nitroso (-NO), -nitro (-NO₂), amino (-NH₂) and alkoxy (-OR) are treated like a substituents.