Trifluoromethylsulfonyl
Triflyl, more formally known as trifluoromethanesulfonyl, is a functional group with the formula F3CSO2–. The triflyl group is often represented by –Tf.
The closely related triflate group (trifluoromethanesulfonate) has the formula F3CSO2O–, and is represented by –OTf.
...
Wikipedia