Q:

Tosyl Chloride? why not anything else

Why do we encounter only Tosyl groups and not anything at the end of the benzene group (ie not to replace the SO2Cl part..rather the Me part at the other end)
I mean something like a CF3 or NO2 would help make it a better leaving group right?

A:

Part of the reason why p-tosyl chloride is seen so often is not only the ease of its preparation, yet that is a side product in the preparation of o-tosyl chloride towards saccharin.  Ease in storage and addition / use are beneficial.  While a p-nosyl chloride eventually may yield a better nucleofuge than the p-tosyl chloride, the very same nitrogroup may ease the hydrolysis of the chloride as well.

