A sulfonyl group can refer either to a functional group found primarily in sulfones or to a substituent obtained from a sulfonic acid by the removal of the hydroxyl group similarly to acyl groups. Sulfonyl groups can be written as having the general formula R-S(=O)₂-R', where there are two  double bonds between the sulfur and oxygen.

A sulfonyl group can refer either to a functional group found primarily in sulfones or to a substituent obtained from a sulfonic acid by the removal of the hydroxyl group similarly to acyl groups. Sulfonyl groups can be written as having the general formula R-S(=O)₂-R', where there are two  double bonds between the sulfur and oxygen.