Acidities of different families of acids are examined in media of different physical and chemical nature: water, acetonitrile (AN), 1,2-dichloroethane (DCE) and the gas phase, with special emphasis on strong acids. Included are OH (carboxylic acids, alcohols, and phenols), NH (sulfonamides, imides), and CH (phenylmalononitriles, etc.) acids as well as HCl, HBr, and HI. Dependence of the acidity trends on moving from water to the gas phase on the nature of the acidity center, and the molecular structure are analyzed. The acidity orders are different in water, AN, DCE, and the gas phase. In some cases the differences are dramatic. AN and DCE display similar acidity order in the set of the investigated acids. It is demonstrated that the decisive factor for the behavior of the acids when transferring between different media is the extent of charge delocalization in the anion and that the recently introduced weighted average positive sigma parameter in spite of its simplicity enables interpretation of the trends in the majority of cases.a Data from Ref [35] if not indicated otherwise. b Reichardt's solvatochromic polarity parameter. [35] c Relative dielectric permittivity at 25 C. d Dipole moment. The first value is expressed in CÁmÁ10 [37] , the second value in Debyes. e The Koppel-Palm solvent basicity parameter [33,34] B and the Kamlet-Taft solvent basicity parameter [36] b. f Estimated value from Ref [37] . g Values from Ref [36] . h The Kamlet-Taft a parameter for solvent hydrogen bond donicity.

A general route to functionalized pentakis(trifluoromethyl)phenyl (C6(CF3)5) derivatives, promising building blocks for designing novel stable carbenes, radical species, superacids, weakly coordinating anions and other practically and theoretically useful species, is presented. This pertrifluoromethylation route proceeds via conveniently pregenerated (trifluoromethyl)copper (CF3Cu) species in DMF, stabilized by addition of 1,3-dimethyl-2-imidazolidinone (DMI). These species react with hexaiodobenzene at ambient temperature to give the potassium pentakis(trifluoromethyl)phenoxide along with hexakis(trifluoromethyl)benzene and pentakis(trifluoromethyl)benzene in a combined yield of 80%. A possible reaction pathway explaining the formation of pentakis(trifluoromethyl)phenoxide is proposed. Pentakis(trifluoromethyl)phenol gives rise to easily functionalized pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)aniline. Pertrifluoromethylation of pentaiodochlorobenzene and pentaiodotoluene allows straightforward access to pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)toluene, respectively. XRD structures of several C6(CF3)5 derivatives were determined and compared with the calculated structures. Due to the steric crowding the aromatic rings in all C6(CF3)5 derivatives are significantly distorted. The gas-phase acidities (Delta Gacid) and pKa values in different solvents (acetonitrile (AN), DMSO, water) for the title compounds and a number of related compounds have been measured. The origin of the acidifying effect of the C6(CF3)5 group has been explored using the isodesmic reactions approach.