text: The prototypical super leaving group is triflate, and the term has come to mean any leaving group of comparable ability. Compounds where loss of a super leaving group can generate a stable carbocation are usually highly reactive and unstable. Thus, the most commonly encountered organic triflates are methyl triflate and alkenyl or aryl triflates, all of which cannot form stable carbocations on ionization, rendering them relatively stable. It has been noted that steroidal alkyl nonaflates (another super leaving group) generated from alcohols and perfluorobutanesulfonyl fluoride were not isolable as such but immediately formed the products of either elimination or substitution by fluoride generated by the reagent. Mixed acyl-trifluoromethanesulfonyl anhydrides smoothly undergo Friedel-Crafts acylation without a catalyst, unlike the corresponding acyl halides, which require a strong Lewis acid. Methyl triflate, however, does not participate in Friedel-Crafts alkylation reactions with electron-neutral aromatic rings.
  Beyond super leaving groups in reactivity lie the "hyper" leaving groups. Prominent among these are λ-iodanes, which include diaryl iodonium salts, and other halonium ions. In one study, a quantitative comparison of these and other leaving groups was conducted. Relative to chloride (k = 1), reactivities increased in the order bromide (k = 14), iodide (k = 91), tosylate (k = 3.7), triflate (k = 1.4), phenyliodonium tetrafluoroborate (, k = 1.2). Along with the criterion that a hyper leaving group be a stronger leaving group than triflate is the necessity that the leaving group undergo reductive elimination. In the case of halonium ions this involves reduction from a trivalent halonium to a monovalent halide coupled with the release of an anionic fragment. Part of the exceptional reactivity of compounds of hyper leaving groups has been ascribed to the entropic favorability of having one molecule split into three.
  Dialkyl halonium ions have also been isolated and characterized for simple alkyl groups. These compounds, despite their extreme reactivity towards nucleophiles, can be obtained pure in the solid state with very weakly nucleophilic counterions such as  and . The strongly electrophilic nature of these compounds engendered by their attachment to extremely labile  (R = alkyl, X = Cl, Br, I) leaving groups is illustrated by their propensity to alkylate very weak nucleophiles. Heating neat samples of  under reduced pressure resulted in methylation of the very poorly nucleophilic carborane anion with concomitant expulsion of the  leaving group. Dialkyl halonium hexafluoroantimonate salts alkylate excess alkyl halides to give exchanged products. Their strongly electrophilic nature, along with the instability of primary carbocations generated from ionization of their alkyl groups, points to their possible involvement in Friedel-Crafts alkylation chemistry. The order of increasing lability of these leaving groups is .