A tosyl group (abbreviate Ts or Tos) combines the toluene and sulfonyl functional groups. The sulfonyl group consists of a hexavalent sulfur atom double bonded to two oxygen atoms and, in the tosylate group, an aromatic ring; an alkyl substituent on the R group forms a sulfonate ester. Thus, the tosylate group is the ester of toluenesulfonic acid. The para orientation illustrated (p-toluenesulfonyl) is most common, and by convention tosyl refers to the p-toluenesulfonate ester.