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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 gas-phase basicity level of ca. 300 kcal/mol (number of phosphorus atoms in the system n ≥ 7), whereas the strongest organic phosphazene ylide superbases are estimated to have (at n ≥ 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 P2 phosphazene...

The solvation, complexation, and disproportionation equilibria, which might be important during titration of a Grignard reagent RMgX with an alcohol in the presence of 1,10-phenanthroline (phen), have been studied both in the gas phase and solution using the density functional theory (DFT) B3LYP/6-31+G* method. Solvation was modeled using the supermolecule approach. NBO atomic charge analyses were performed at the B3LYP/6-31G* level. The absorption spectra of the complexes were calculated by the DFT TD/MPW1PW91/6-311+G** method. According to our calculations the complexation of magnesium halide MgX2 with 1,10-phenanthroline is the reason for the disappearance of the red color of the complex RMgX(phen) near the titration end point.

The conformational analysis of 1-acetyl-2-methylhydrazine was performed using DNMR spectroscopy and quantum chemical calculations (B3LYP/6-31+G*, AM1 and PM3). Activation barrier for interconversion of Z and E conformers was measured to be 16.1 kcal/mol by DNMR. DFT calculations indicate that there are four minima on the 1-acetyl-2-methylhydrazine potential energy surface and the most stabile is Z conformer with the hydrogen bond between carbonyl group oxygen and hydrogen at non-amide nitrogen. The amide nitrogen was found to be close to planar in minima but strongly pyramidalized in TS. The activation barriers calculated at B3LYP/6-31+G* level of theory were in good agreement with experimentally measured one. AM1 method with molecular mechanics correction gave potential energy surface in reasonable agreement with DFT results, but the activation energies were strongly underestimated. PM3 method was found to give unsatisfactory results for conformational analysis of 1-acetyl-2-methylhydrazine.

Coupled cluster and DFT B3LYP calculations have been used to determine the structures, heats of formation, and gas-phase basicities of alkaline metal oxides M2O and hydroxides MOH, where M=Li, Na and K. Structures calculated at CCSD(T,Full)/6-31++G(2df,2pd), B3LYP/6-311+G∗∗, and B3LYP/6-311+G(3df,3pd) levels of theory were in a good agreement with each other and available experimental estimates. Atomic charges and the Bader's topological charge density analysis indicate that the bonding between M and O is ionic in all studied species. Calculated heats of formation were used to discriminate between different experimental values. Proton affinities of 1193, 1319 and 1374 kJ/mol are suggested for Li2O, Na2O, and K2O, respectively.

The molecular geometries of polyyne chains H(CC)nH with their deprotonated forms (anions) have been optimized using ab initio LCAO-SCF molecular orbital (MO) method and density functional theory at different basis set levels. The polyynes possess a series of alternating single and triple bonds. On the theoretical side the persistence of bond alternation and the effect of chain lengthening on the individual bond length in linear conjugated polyyne chains has been investigated. The common conclusion has been drawn that the bond alternation will persist and that bond length variation will be small. The triple bond length increases progressively toward the asymptotic limits as the value of n increases progressively. If the split-valence basis set was employed, the total charges obtained using the Mulliken population analysis yielded unrealistic values. Using natural bond orbital (NBO) analysis or Bader's analysis, the net charges of the individual atoms converge very rapidly to their asymptotic limits, and the central atoms have almost zero charges in contrast to the Mulliken population analysis results. The reliability of deprotonation energies of neutral polyynes and their monoanionic derivatives calculated from the differences in molecular energy of the parent chains and the corresponding anions E(H(CC)n−)–E(H(CC)nH) and E(−(CC)n−)–E(H(CC)n−) was tested for different basis sets. The increase of the number of CC bonds in the chain decreases these differences asymptotically. The studied compounds are the best available building blocks in bimetallic compounds with useful properties in molecular electronics and nonlinear optics. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 73–85, 2001

Acidities of simple saturated hydrocarbons were studied using ab initio G2 and CCSD(T)/6-311+G ∗∗ , and DFT B3LYP/6-311+G ∗∗ calculations. The results suggest a 1.4 kcal/mol lower basicity for the isopropyl anion relative to the current experimental value. Charge densities of the studied neutrals, anions, and radicals were analyzed using Bader's topological charge density analysis. The acidity trends in saturated hydrocarbons were rationalized based on substituent electronegativity (field/inductive) and polarizability effects.

The gas-phase acidities and basicities for 49 acids and 32 bases, calculated using B3LYP hybrid DFT method and 6-31G ∗ , 6-31+G ∗ , 6-311+G ∗∗ , and 6-311+G(3df,3pd) basis sets are compared with corresponding experimental values. The best results were obtained with 6-311+G(3df,3pd) basis set; the average absolute errors were below 2.5 kcal/mol both for basicities and acidities. Good results for both acidities and basicities (the average absolute errors were ⩽3 kcal/mol) were also obtained using the 6-311+G ∗∗ basis set and even with a moderate 6-31+G ∗ basis set (mean absolute errors were

The electrostatic explanation of Siggel and Thomas for the acidity differences between series of acids was investigated critically. Acidities and electrostatic potentials at the protons of XOH, XNH 2 , and XCH 3 derivatives (X=H, CH 3 , HCO, NO 2 , and F) were calculated at the Becke3LYP/6-311+G ∗∗ level. Final state (anion) relaxation energies were obtained as proposed by Siggel and Thomas. Examination of initial and final state contributions revealed deficiencies in the Siggel–Thomas method as the final-state (relaxation) energies still retain contributions from the electronic structure of the initial state. Hence, this relaxation energy is not reliable as a measure of resonance stabilisation in anion. The application of Siggel–Thomas approach in two opposite directions—dissociation of neutral acid and protonation of an anion—leads to contradictory conclusions about whether the acidity difference between methanol and formic acid is determined by the neutral acid or anion. Hence, this scheme cannot be used to determine the initial state (neutral acid) and final state (anion) contributions to acidity as proposed by Siggel and Thomas.

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 Bronsted acids, Bronsted−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 Bronsted 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 ΔGacid values obtained this way can be used as the substitutes for the u...

The previously reported gas-phase lithium cation basicity (LCB) scale (Taft et al. Pure Appl. Chem. 1990, 62, 17) was revised on the basis of recent experimental and theoretical (G2 calculations) results. A new anchoring based on the experimental LCA value for H2O is suggested (all earlier reported values of LCB should be reduced by 2.6 kcal/mol). New LCBs for 28 compounds were measured using FT-ICR, and a revised LCB scale now extended to 205 compounds is given. Correlations between gas-phase basicities toward lithium cation and proton were examined. Though a general trend is discernible, fair correlations are obtained provided that separate lines are drawn for homogeneous families. The differences in slopes are traced back to the different sensitivities to structural effects. Large deviations are explained by either a different attachment center for Li+ and H+ or a chelation effect toward Li+. G2 and G2(MP2) calculations of LCBs for a wide selection of 37 compounds and density functional theory (B3LYP/6...

Acidities and homolytic O−H bond dissociation energies of CHnF3-nOH and CHnF3-nSH (n = 0−3) were calculated at the G2 level of theory. The variation of the geometry of the neutral species and products of heterolytic and homolytic proton abstraction processes, as well as the energetics (gas-phase acidities and homolytic bond dissociation energies of the title compounds), upon successive fluorine substitution has been studied. The results show that the progressive introduction of fluorine atoms into methanol and methanethiol reduces significantly the acidity gap between the representatives of these two series. Therefore, the calculations indicate that the acidities of CF3OH and CF3SH are predicted to be rather close: the former compound is expected to be 0.1 kcal/mol more acidic than its SH counterpart. It was concluded that negative (anionic) hyperconjugation and electrostatic effects are mainly responsible for such behavior.

The possibility to predict the stability constants of the complexes of magnesium, zinc, cadmium, and lead cations with anions of different carboxylic acids by PM3 calculations was investigated. Linear correlation between calculated complex-formation reaction enthalpies and experimentally measured stability constants were obtained for complexes of each metal, while the overall correlation was not satisfactory. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 653–658, 1997

It is usually believed that relativistic effects as described by the Dirac-Schrödinger equation (relative to the classical or time-independent Schrödinger equation) are of little importance in chemistry. A closer look, however, reveals that some important and widely known properties (e.g., gold is yellow, mercury is liquid at room temperature) stem from relativistic effects. So far the influence of relativistic effects on the acid-base properties has been mostly ignored. Here we show that at least for compounds of gold such omission is completely erroneous and would lead to too high basicity and too low acidity values with errors in the range of 25-55 kcal mol(-1) (or 20 to 44 powers of ten in pK(a) units) in the gas-phase. These findings have important implications for the design of new superstrong acids and bases, and for the understanding of gold-catalysed reactions.

The interaction between the cesium cation and fulvic or humic acids is supposed to play a role in cesium mobility in the environment, which is of importance in the context of geographical dispersion or concentration of the corresponding radionuclides. Among the singly charged positive clusters generated by electrospray ionization of mixtures of carboxylic acids (AH) and cesium salts (nitrate, iodide, or trifluoroacetate), the cluster [A

Quantum chemical calculations of potentially superacidic neutral Bronsted acids were carried out using the PM3 method. It was shown that the PM3 method can be used to predict the gas phase acidities of acidic compounds only if empirical corrections are made. A strong acidifying effect is predicted for a new family of compounds in which an sp2 oxygen is substituted by an (DOUBLE BOND) NSO2CF3 group. So, for example, such replacement is expected to result in acid strengthening by 47.5 kcal/mol in the case of CH3CHO and by 22.7 kcal/mol in the case of CF3SO2OH. The acidities of such compounds are predicted to be increased further (nonadditively) by stepwise replacements of (DOUBLE BOND) O by (DOUBLE BOND) NSO2CF3. The geometries of known superacidic systems were reproduced quite well by PM3 method. The geometries of several superacidic systems were analyzed. © 1996 by John Wiley & Sons, Inc.

Complexes of dimethyl sulfoxide with F-, Cl-, OH-, CH3O-, HCOO-, and NO2- anions were studied at MP2/6-31+G* and B3LYP/6-31+G* levels of theory. The energies, geometries, NBO charges, and topologic...

The aromaticity of several heterosubstituted cyclopropenes and corresponding protonated forms was investigated using ab initio calculations at the G2-MP2 level of theory, topological charge density, and NBO analysis. It was shown that according to geometric, energetic, charge density, and magnetic criteria these systems are remarkably aromatic, especially the protonated forms. It was shown that the aromatic delocalization of double bond in the cyclopropene ring can be well modeled using a three-center two-electron bond in the framework of NBO analysis proposed by Reed and Weinhold.

An approach to the quantitative evaluation of XOH acidity in the gas phase and in dimethyl sulphoxide solution is described. It is based on one-parameter correlations between the acidities of XOH family members and the electron affinities of the XO radicals or highest occupied molecular orbitals (HOMO) energies of the correspondging XO− anions. The approach is based on Koopmans' theorem and provides familial correlations for the acidities of alcohols, carboxylic acids, phenols and mineral acids with calculated (MNDO, AM1 or PM3) HOMO energies of their anions.

International audience; A Fourier transform ion cyclotron resonance spectrometry (FT-ICR) study of the gas-phase protonation of ammonia-borane and sixteen amine/boranes R(1)R(2)R(3)N-BH(3) (including six compounds synthesized for the first time) has shown that, without exception, the protonation of amine/boranes leads to the formation of dihydrogen. The structural effects on the experimental energetic thresholds of this reaction were determined experimentally. The most likely intermediate and the observed final species (besides H(2)) are R(1)R(2)R(3)N-BH(4)(+) and R(1)R(2)R(3)N-BH(2)(+), respectively. Isotopic substitution allowed the reaction mechanism to be ascertained. Computational analyses ([MP2/6-311+G(d,p)] level) of the thermodynamic stabilities of the R(1)R(2)R(3)N-BH(3) adducts, the acidities of the proton sources required for dihydrogen formation, and the structural effects on these processes were performed. It was further found that the family of R(1)R(2)R(3)N-BH(4)(+) ions is characterized by a three-center, two-electron bond between B and a loosely bound H(2) molecule. Unexpected features of some R(1)R(2)R(3)N-BH(4)(+) ions were found. This information allowed the properties of amine/boranes most suitable for dihydrogen generation and storage to be determined.

The prototropic tautomerism and acidity of (FSO2)3CH was studied at both the semiempirical (PM3) and ab initio (HF/STO-3G∗ and 3–21G∗) level. It was shown that PM3 fails to describe the energetics of prototropic tautomerism, while giving the geometry of the sulfo form in good agreement with the experimental data. The ab initio calculations predict, in accordance with the experiment, that the sulfone form is more stable than the enol form. The conformity between calculated and experimental geometry was also satisfactory. The gas phase acidity of (FSO2)3CH was calculated and the factors which contribute to the extremely high gas phase acidity of the title compound were discussed.

Ab initio (TZV*, SBK*, and 3–21G* or 6–31G* basis sets) calculations were performed to predict the geometries and gas-phase proton affinities of Li2O, LiOH, LiNH2, Na2O, NaOH, NaNH2, K2O, KOH, and KNH2. © 1994 John Wiley & Sons, Inc.

The Sonogashira cross-couplig reaction, consisting of oxidative addition, cis-trans isomerization, transmetalation, and reductive elimination, was computationally modeled using the DFT B3LYP/cc-pVDZ method for reaction between bromobenzene and phenylacetylene. Palladium diphosphane was used as a catalyst, copper(I) bromide as a co-catalyst and trimethylamine as a base. The reaction mechanism was studied both in the gas phase and in dichloromethane solution using PCM method. The complete catalytic cycle is thermodynamically strongly shifted toward products (diphenylacetylene and regenerated palladium catalyst) and is exothermic being in accordance with experimental data. The rate-determining step is the oxidative addition, since the highest point on the Gibbs energy graph of the complete reaction is the transition state of this step. This conclusion is also supported by recent experimental data. The computed energy profile suggests that the transmetalation step is initiated by the dissociation of neutral ligand, while the activation Gibbs energy of this step is 0.1 kcal mol(-1) in the gas phase.

Gas-phase acidities have been calculated for 175 compounds using the PM3 semiempirical molecular orbital model. With some exceptions, PM3 seems to be a useful tool for the investigation of gas-phase acidities. The main problems encountered involve two rather different classes of acids: one which generates small anions (e.g., halide ions, hydride ion, etc.), in which the charge is localized on one atom, and, a second, represented by anions that contain bulky electron acceptor substituents characterized by an extensive negative charge delocalization. In some cases (anilines, amides, alcohols, and phenols) the average error in predicted gas-phase acidity can be significantly reduced by employing an empirically derived correction. Comparison with AM1 results shows that both methods are of roughly equal quality with the exception of hypervalent molecules where PM3 is better (averaged unsigned errors are 11.8 and 17.0 kcal/mol for PM3 and AM1, respectively).

The AM1 and PM3 methods with the inclusion of a limited configuration interaction (CI) approach were used to study the stabilities of the tautomers of hexafluoroacetylacetone (HFAA). It was found that the most stable tautomer is the hydrogen bonded cyclic asymmetric enol form, the energy of which is lower than that of any keto tautomer by at least 2.5 kcal mol−1 with the AM1 model and 0.9 kcal mol−1 with the PM3 model. It was shown that HFAA should be an O-H acid. The intramolecular hydrogen bond energy is 4.5 kcal mol−1 with the AM1 model and 4.8 kcal mol−1 with the PM3 model. It was shown that proton transfer from one oxygen atom to the other is controlled by the double minimum potential curve and the correspondig energy barrier height is 24.1 kcal mol−1 with the AM1 model and 27.4 kcal mol−1 with the PM3 model.

The possible reaction pathways between methyllithium and disubstituted 1,2,4,5-tetrazines (bearing methyl, methylthio, phenyl, and 3,5-dimethylpyrazolyl groups) were investigated by means of the density functional theory B3LYP/6-31G* method. Solvation was modeled using the supermolecule approach, adding one tetrahydrofuran molecule to the complexes. Comparison of the calculated energies and structures for the alternate azaphilic and nucleophilic addition pathways showed that the azaphilic addition is kinetically favored over nucleophilic addition, while thermodynamically the nucleophilic addition is usually preferred. The coordination of the tetrazine molecule with methyllithium was found to play a crucial role in the process. These findings provide the first rationale for the experimentally observed unique reactivity of tetrazines toward polar organometallic reagents, suggesting the presence of a kinetically controlled process.

The AM1 and PM3 methods with the inclusion of a limited configuration interaction (CI) approach were used to study the stabilities of the tautomers of hexafluoroacetylacetone (HFAA). It was found that the most stable tautomer is the hydrogen bonded cyclic asymmetric enol form, the energy of which is lower than that of any keto tautomer by at least 2.5 kcal mol−1 with the AM1 model and 0.9 kcal mol−1 with the PM3 model. It was shown that HFAA should be an O-H acid. The intramolecular hydrogen bond energy is 4.5 kcal mol−1 with the AM1 model and 4.8 kcal mol−1 with the PM3 model. It was shown that proton transfer from one oxygen atom to the other is controlled by the double minimum potential curve and the correspondig energy barrier height is 24.1 kcal mol−1 with the AM1 model and 27.4 kcal mol−1 with the PM3 model.

The aromaticity of several heterosubstituted cyclopropenes and corresponding protonated forms was investigated using ab initio calculations at the G2-MP2 level of theory, topological charge density, and NBO analysis. It was shown that according to geometric, energetic, charge density, and magnetic criteria these systems are remarkably aromatic, especially the protonated forms. It was shown that the aromatic delocalization of double bond in the cyclopropene ring can be well modeled using a three-center two-electron bond in the framework of NBO analysis proposed by Reed and Weinhold.

International audience; Collision-induced dissociation (CID) of the Cs(+) heterodimer adducts of the nitrate anion (NO(3)(-)) and a variety of substituted benzoates (XBenz(-)) [(XBenz-)(Cs(+))(NO(3)(-))](-) produces essentially nitrate and benzoate ions. A plot of the natural logarithm of their intensity ratio, In(I(NO(3)(-)/I(XBenz(-))], versus the calculated cesium cation affinity (OFT B3LYP) of the substituted benzoate ions (equivalent to the enthalpy of heterolytic dissociation of the salt) is reasonably linear. This suggests that the kinetic method can be used as a source of data on the intrinsic interaction between the anionic and the cationic moieties in a salt. Copyright (C) 2010 John Wiley & Sons, Ltd.

The gas-phase cesium cation affinities (CsCAs) and basicities (CsCBs) for 56 simple neutral compounds (mostly aromatic molecules) and 41 anions (carboxylates and phenolates) were calculated using density functional theory (DFT), in the context of the interaction of Cs(+) with soil organic matter (SOM). The B3LYP/def2-TZVP method gives in general CsCAs and CsCBs in a good agreement with experimental data. The strong deviations in case of NO(3)(-) and CsSO(4)(-) anions need further experimental investigations as the high-level CCSD(T) calculations support B3LYP results. Different cesium cation complexation patterns between Cs(+) and the neutral and anionic systems are discussed. As expected, the strongest CsCAs are observed for anions. The corresponding quantities are approximately by 4-5 times higher than for the neutral counterparts, being in the range 90-118 kcal/mol. The weakest cesium cation bonding is observed in the case of unsubstituted aromatic systems (11-15 kcal/mol).

Absolute (nonrelative) pKa calculations for substituted phenols were carried out in nonaqueous media, demonstrating the predictive power of the integral equation formalism PCM method with a mean unsigned error of 0.6 pKa units for DMSO and 0.7 pKa units for MeCN at the B3LYP/6-31+G** level of theory combined with the scaled B3LYP/6-311+G** gas-phase data. At the same time, the correlation between the calculated and experimental pKa values yielded the value of the linear regression slope very close to unity for both DMSO and MeCN. Computation of pKa of neutral acids in nonaqueous solutions with a reasonable precision obviously depends on carefully tuned cavities, optimized for nonaqueous solutions. The ability of continuum solvation model to compensate charge escape from the cavity, which is prominent in the case of anions, is also required. And finally, good quality gas-phase data is essential to achieve required pKa precision.

Humic substances (HS), including humic and fulvic acids, play a significant role in the fate of metals in soils. The interaction of metal cations with HS occurs predominantly through the ionized (anionic) acidic functions. In the context of the effect of HS on transport of radioactive cesium isotopes in soils, a study of the interaction between the cesium cation and model carboxylic acids was undertaken. Structure and energetics of the adducts formed between Cs+ and cesium carboxylate salts [Cs+RCOO−] were studied by the kinetic method and density functional theory (DFT). Clusters generated by electrospray ionization mass spectrometry from mixtures of a cesium salt (nitrate, iodide, trifluoroacetate) and carboxylic acids were quantitatively studied by CID. By combining the results of the kinetic method and the energetic data from DFT calculations, a scale of cesium cation affinity, CsCA, was built for 33 cesium carboxylates representing the first scale of cation affinity of molecular salts. The structural effects on the CsCA values are discussed.

DFT B3LYP/6-311+G** calculations were performed to study the proton and lithium cation binding to the acetylacetone, hexafluoroacetylacetone, diacetamide, and hexafluorodiacetamide. It was shown that the most stable Li+ adduct always corresponds to cyclic complex based on the trans, trans-keto form of the base. The product of protonation was found to be similar trans, trans-keto form based cyclic structure in case of diacetamide and hexafluorodiacetamide, while for acetylacetone and hexafluoroacetylacetone the protonation simply involves the addition of proton to (free) carbonyl oxygen in already cyclic enol form of the base with possible rotation of O−H bond.

The Li+ cation complexes with one and two CO molecules have been studied computationally. The calculations reveal the conditions when two CO molecules could bind to one Li+ cation in zeolite Li-ZSM-5. In the absence of dicarbonyls (at low adsorbate coverage or at high temperatures), the IR absorption bands can be assigned only on the basis of the Li+ coordination number to the framework oxygen atoms.

In relation to the interaction between 137 Cs and soil organic matter, electrospray mass spectrometry experiments and density functional theory (DFT) calculations were carried out on the dissociation of positively charged adducts formed by cesium nitrate and cesium organic salts attached to a cesium cation [Cs(CsNO 3 )(CsA)] + (A = benzoate, salicylate, hydrogen phthalate, hydrogen maleate, hydrogen fumarate, hydrogen oxalate, and hydrogen malonate ion). These mixed clusters were generated by electrospray from methanol solutions containing cesium nitrate and an organic acid. Collision-induced dissociation of [Cs(CsNO 3 )(CsA)] + in a quadrupole ion trap gave [Cs(CsNO 3 )] + and [Cs(CsA)] + as major product ions. Loss of HNO 3 was observed, and also CO 2 loss in the case of A = hydrogen malonate. Branching ratios for the dissociation into [Cs(CsNO 3 )] + and [Cs(CsA)] + were treated by the Cooks' kinetic method to obtain a quantitative order of bonding energetics (enthalpies and Gibbs free energies) between Cs + and the molecular salt (ion pair) CsA, and were correlated with the corresponding values calculated using DFT. The kinetic method leads to relative scales of Cs + affinities and basicities that are consistent with the DFT-calculated values. This study brings new data on the strong interaction between the cesium cation and molecular salts CsA.

A generalized principle of designing superstrong Brønsted acids is suggested according to the following scheme: M=O --M=Z(X)(n). It consists of the formal replacement of =O fragment in carbonyl, sulfonyl, etc. groups in various acidic systems (e.g., CH(3)CHO, FSO(3)H, where M is the CH(3)CH= or FSO(2)H=fragment, respectively) by =NSO(2)F, =NCN, =C(CN)(2), =P(SO(2)F)(3), =S(CN)(4), or any other formally bivalent group =Z(X)(n) (where the formal valency of the central atom Z is n + 2), leading to highly acidic systems (e.g., HC(=P(CN)(3))NH(2), FS(=C(CN)(2))(2)OH, etc.). It is demonstrated that in several cases the introduction of the double-bonded substituent at the central atom (e.g., N, C, P, S, Cl) that carries the potentially acidic proton or the acidity site (e.g., OH, NH(2), CH(3), etc. groups) will lead to the enormous (up to ca. 120 kcal/mol or 88 pK(a) units!) increase of the intrinsic acidity of the respective parent acid. The acidity of the resulting acids and the scope and limitations of the principle are explored using density functional theory calculations at B3LYP 6-311+G level. Some of the resulting acids (or their anions) were found to undergo fragmentation in the course of the geometry optimization. The general trend that follows from the results of the calculations is that the stability of the resulting compounds is influenced by both the M and the Z. If M is a first row element (carbon or nitrogen), then stable species are produced with almost any Z. If M is a second row element (sulfur or phosphorus), then the species with first row Z are mostly predicted to be stable, but most of the species with second row Z are expected to undergo fragmentation during the geometry optimization. The Z = N and Z = C derivatives (e.g., =NSO(2)CF(3), =C(CN)(2), =C(SO(2)CF(3))(2), etc.) are predicted to be the most stable. However, they have relatively modest electron-accepting power as compared to their penta-, hexa-, and heptavalent counterparts. The acidifying effects of the =Z(X)(n)() groups with the same X increase with increasing n: =NCN=C(CN)(2)=P(CN)(3)=S(CN)(4) and =NSO(2)F=C(SO(2)F)(2)=P(SO(2)F)(3). Also, the acidifying effect of a fluorosulfonyl-substituted substituent is higher than that of the corresponding cyano-substituted substituent.

The sec-butylammonium salt catalysed oxidative addition of phenyl bromide to tris(triphenylphosphane)palladium and reaction of phenylacetylene with cis-Pd(PPh3)2(Ph)Br were modelled using DFT B97D/cc-pVDZ method to study the mechanism of the copper-free Sonogashira cross-coupling reaction. sec-Butylammonium bromide influences the oxidative addition by coordinating with palladium catalyst and the resulting product is trans-Pd(PPh3)2(Ph)Br, not the corresponding cis-compound, which is formed in the absence of salt. The transition-state energy of this oxidative addition mechanism is very close to the previously reported biligated oxidative addition pathway. Reaction of acetylene with cis-Pd(PPh3)2(Ph)Br can lead to either a transor a cis-Pd(PPh3)2(CCPh)Ph complex, while only the latter is capable of undergoing reductive elimination.

The three-layer ONIOM(B3LYP/6-311+G**:HF/3-21G*:MNDO) method was used to model the structural, energetic, and spectroscopic (IR and 1H NMR) properties of the acid sites (types 1 and 2) of zeolite ZSM-5. The calculation method used reproduced the properties of studied acid sites well. In the case of the second type of Bronsted acid site, the hydrogen of the bridged hydroxyl group forms a hydrogen bond with the next nearest oxygen to the aluminum atom. The analysis of experimental IR and 1H NMR spectra in combination with current calculations suggests that the experimentally observable mean acidity of zeolite ZSM-5 depends on temperature because the occupancies of protons at various oxygen sites are kinetically controlled and thermodynamic equilibrium is reached at high temperatures.

Structure-activity relationships in a data set of HPV6-E1 helicase ATPase inhibitors were investigated based on two different sets of descriptors. Statistically significant four parameter Quantitative Structure-Activity Relationships (QSAR) models were constructed and validated in both cases (R 2 =0.849; R 2 cv =0.811; F=52.20; s 2 =0.25; N=42). A Fragment based QSAR (FQSAR) approach was applied for developing a fragment-QSAR equation, which enabled the construction of virtual structures for novel ATPase inhibitors with desired or pre-defined activity.

Basicity of Organic Superbases with Vinamidine Structure in Gas Phase and Acetonitrile – A DFT Study