In the case of polyfunctional compounds, one of the functional groups is chosen as the principal functional group and the compound is then named on that basis. The remaining functional groups, which are subordinate functional groups, are named as substituents using the appropriate prefixes. The choice of principal functional group is made on the basis of order of preference. The order of decreasing priority for some functional groups is:

$-\mathrm{COOH}, –{\mathrm{SO}}_3\mathrm{H}, -\mathrm{COOR} (\mathrm{R}=\mathrm{alkyl} \mathrm{group}), \mathrm{COCl}, -{\mathrm{CONH}}_2, -\mathrm{CN}, -\mathrm{HC}=\mathrm{O}, >\mathrm{C}=\mathrm{O}, -\mathrm{OH}, -{\mathrm{NH}}_2, >\mathrm{C}=\mathrm{C}<, -\mathrm{C}\equiv \mathrm{C}-.$

 

For example, the IUPAC name of

${\mathrm{HOCH}}_2({\mathrm{CH}}_2{)}_3{\mathrm{CH}}_2{\mathrm{COCH}}_3$ is 7-hydroxyheptan-2-one.

The correct decreasing order of priority of given functional groups is

$-{\mathrm{SO}}_3\mathrm{H}>-\mathrm{COCl}>-{\mathrm{CONH}}_2>-\mathrm{CN}$