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The structure of a typical sulfonate group.

A sulfonate ion is an ion that contains the -S(=O)2-O functional group. The general formula is RSO2O, where R is some organic group. They are conjugate bases of sulfonic acids with formula RSO2OH.

Sulfonates, being weak bases, are good leaving groups in Sn1, Sn2, E1 and E2 reactions.

As is common, the same term is used for compounds containing this functional group, ionic salts, or similar covalent compounds, esters.


  • Mesylate (methanesulfonate) ion, CH3SO2O
  • Triflate (trifluoromethanesulfonate) ion, CF3SO2O
  • Tosylate (p-toluenesulfonate) ion, CH3C6H4SO2O
  • Besylate (benzenesulfonate) ion, C6H5SO2O

See Also

The preceding terms apply to salts and esters as well as anions. fi:Sulfonaatti