and strengthening the proton donating ability of the solution. For example, fluoroantimonic acid, nominally (), can produce solutions with a H0 lower than –21, giving it a protonating ability over a billion times greater than 100% sulfuric acid. Fluoroantimonic acid is made by dissolving antimony pentafluoride (SbF5) in anhydrous hydrogen fluoride (HF). In this mixture, HF releases its proton (H+) concomitant with the binding of F− by the antimony pentafluoride. The resulting anion () delocalizes charge effectively and holds onto its electron pairs tightly, making it an extremely poor nucleophile and base. The mixture owes its extraordinary acidity to the weakness of proton acceptors (and electron pair donors) (Brønsted or Lewis bases) in solution. Because of this, the protons in fluoroantimonic acid and other superacids are popularly described as "naked", being readily donated to substances not normally regarded as proton acceptors, like the C–H bonds of hydrocarbons. However, even for superacidic solutions, protons in the condensed phase are far from being unbound. For instance, in fluoroantimonic acid, they are bound to one or more molecules of hydrogen fluoride. Though hydrogen fluoride is normally regarded as an exceptionally weak proton acceptor (though a somewhat better one than the SbF6– anion), dissociation of its protonated form, the fluoronium ion H2F+ to HF and the truly naked H+ is still a highly endothermic process (ΔG° = +113 kcal/mol), and imagining the proton in the condensed phase as being "naked" or "unbound", like charged particles in a plasma, is highly inaccurate and misleading. More recently, carborane acids have been prepared as single component superacids that owe their strength to the extraordinary stability of the carboranate anion, a family of anions stabilized by three-dimensional aromaticity, as well as by electron-withdrawing group typically attached thereto. In superacids, the proton is shuttled rapidly from proton acceptor to proton acceptor by tunneling through a hydrogen bond via the Grotthuss mechanism, just as in other hydrogen-bonded networks, like water or ammonia. Applications In petrochemistry, superacidic media are used as catalysts, especially for alkylations. Typical catalysts are sulfated oxides of titanium and zirconium or specially treated alumina or zeolites. The solid acids are used for alkylating benzene with ethene and propene as well as difficult acylations, e.g. of chlorobenzene. Examples The following values show the Hammett acidity function for several superacids, the strongest being fluoroantimonic acid. Increased acidity is indicated by smaller (in this case, more negative) values of H0.