For the first time G2 or G2(MP2) calculations or both have been performed to calculate the acidity and deprotonation enthalpy of classical strong mineral acids HClO4, CF3SO3H, FSO3H, H2SO4, HBF4, HPO3, and HNO3. Also, the intrinsic acidities and gas-phase deprotonation enthalpies for 39 neutral strong or superstrong Brønsted acids, Brønsted−Lewis conjugate acids, and some compounds modeling the acidic clusters of zeolites were calculated using the DFT B3LYP 6-311+G** approach. DFT B3LYP method at 6-31+G* basis was used for the calculation of the intrinsic Brønsted acidities of the conjugate acids of the carborane anion CB11H12 - and its mono-, hexa-, and dodecafluorinated analogues. G2 and G2(MP2) theories describe the acidities of different compounds better than DFT B3LYP//6-311+G**. However, the DFT results could also be used for the estimation of the acidity of compounds which are out of reach of G2 or G2(MP2) theory. The estimated ΔG acid values obtained this way can be used as the substitutes for the unavailable experimental values, especially for those (rather numerous) compounds for which the experimental determination of ΔG acid is very difficult. In the case of practically all considered families of compounds extremely high acidities (low ΔG acid values) could be reached. If the compounds were started from HF as the parent acid, then the estimated ΔG acid as low as 249.0 kcal/mol (for F(OSO2)4H) could be reached by formation of Brønsted−Lewis conjugate acids by consecutive complexation with SO3 molecules. Also very low ΔG acid value (ΔG acid(HSbF6) = 255.5) could be reached by complexation of HF with SbF5. At least as high intrinsic acidities as in case of the strongest Brønsted−Lewis superacids could be reached in the case of progressive introduction of highly electronegative, correctly oriented polarizable dipolar electron-accepting substituents into the acidity site. Indeed, the introduction of five CN groups into cyclopentadiene is expected to lead to the acidity ΔG acid = 250.1 kcal/mol which is lower than the corresponding quantity even for hexafluoroantimonic acid (ΔG acid = 255.5 kcal/mol). However, by far the strongest intrinsic Brønsted acidity (ΔG acid = 209 kcal/mol) for dodecafluorosubstituted carborane acid CB11F12H is predicted to exceed the intrinsic acidity of sulfuric acid by about 90 kcal/mol or by almost 70 powers of ten, whereas semi-empirical PM3 calculations suggest that the conjugate acid of the dodecatrifluoromethylmonocarborane anion CB11(CF3)12 - could be the first neutral Brønsted superacid whose acidity (deprotonation energy) is expected to be below the landmark 200 kcal/mol level. An approximate linear relationship is found to hold between the calculated gas-phase acidities of strong and superstrong Brønsted acids and the corresponding Hammett acidity functions of the corresponding neat acids. The simultaneous existence of the widely overlapping areas on the gas-phase acidity scale of neutral and cationic Brønsted acids evidences strongly for the feasibility of the spontaneo...

A density functional theory (B3LYP/6-311+G**), ab initio (HF/3-21G*), and semiempirical (PM3) study of intrinsic basicities, protonation energies, or protonation enthalpies of organic phosphorus imine (iminophosphorane) including phosphazene, phosphorus ylide (phosphorane), and phosphine superbases has been performed. The study shows that representatives of the first two classes of the above-mentioned organic superbases can reach the basicity level of the strongest inorganic superbases such as alkali-metal hydroxides, hydrides, and oxides. The strongest organic phosphazene imine superbases are predicted to reach the gasphase basicity level of ca. 300 kcal/mol (number of phosphorus atoms in the system n g 7), whereas the strongest organic phosphazene ylide superbases are estimated to have (at n g 5) gas-phase basicities around or beyond 310-320 kcal/mol. The phosphine superbases, including the Verkade's bicyclic phosphines (proazaphosphatranes) are predicted to have a basicity comparable to P 2 phosphazenes or P 1 phosphorus ylides, whereas the respective proazaphosphatrane imines and ylides are expected to be the strongest organic superbases which contain only a single phosphorus atom. Extremely high expected basicity values and handling preferences over inorganic superbases make representatives of novel organic superbases possible partners for observing the spontaneous gas-phase proton transfer between neutral Brønsted superacids and -bases. For the comparison, the basicities of some alkali-metal substituted ammonia, phosphine, phosphorus, and nitrogen ylides and imines have been also calculated.

Seventeen superbasic phosphazenes and two Verkade's bases were used to supplement and extend the experimental gas-phase basicity scale in the superbasic region. For 19 strong bases the gas-phase basicity values (GB) were determined for the first time. Among them are such well-known bases as BEMP (1071.2 kJ/mol), Verkade's Me-substituted base (1083.8 kJ/mol), Et-N=P(NMe2)2-N=P(NMe2)3 (Et-P2 phosphazene, 1106.9 kJ/mol), and t-Bu-N=P(NMe2)3 (t-Bu-P1 phosphazene, 1058.0 kJ/mol). For the first time experimental GB values were determined for P2 phosphazenes. Together with our previous results self-consistent experimental gas-phase basicity scale between 1020 and 1107 kJ/mol is now established. This way an important region of the gas-phase basicity scale, which was earlier dominated by metal hydroxide bases, is now covered also with organic bases making it more accessible for further studies. The GB values for several superbases were calculated using density functional theory at the B3LYP/6-311+G** level. For the phosphazene family the standard deviation of the correlation between the experimental and theoretical values was 6.5 kJ/mol.