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Alkylation of nitroarenes via Vicarious Nucleophilic Substitution (VNS) was tested experimentally and modelled with DFT calculations. Mechanistic studies reveal intrinsic differences between reactions of archetypal carbanion precursor PhSO

The physicochemical properties and the synthesis of four α-pinene oxidation products, terebic acid, 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), diaterpenylic acid acetate (DTAA), and pinanediol, are presented in this study. The physicochemical properties encompass thermal properties, solubility in water, and dissociation constant (pKa) for the investigated compounds. It was found that terebic acid exhibits a relatively high melting temperature of 449.29 K, whereas pinanediol revealed a low melting temperature of 329.26 K. The solubility in water was determined with the dynamic method and the experimental results were correlated using three different mathematical models: Wilson, NRTL, and UNIQUAC equations. The results of the correlation indicate that the Wilson equation appears to work the best for terebic acid and pinanediol. The calculated standard deviation was for 3.79 for terebic acid and 1.25 for pinanediol. In contrast, UNIQUAC was the best mathematical model for DTAA and MBTCA. The calculated standard deviation was 0.57 for DTAA and 2.21 for MBTCA. The measured water solubility increased in the following order: pinanediol > DTAA ≥ MBTCA > terebic acid, which affects their multiphase aging chemistry in the atmosphere. Moreover, acidity constants (pKa) at 298, 303, and 308 K were determined for DTAA with the Bates–Schwarzenbach spectrophotometric method. The pKa values obtained at 298, 303, and 308 K were found to be 3.76, 3.85, and 3.88, respectively.

Here, the study is focused on the synthesis and determination of physicochemical properties of four α-pinene secondary organic aerosol (SOA) products: cis-pinic acid, cis-pinonic acid, cis-norpinic acid, and cis-norpinonic acid. These encompass their thermal properties, solid-liquid phase equilibria, and dissociation constant (pKa). Thermal properties, including the melting temperature, enthalpy of fusion, temperature, and enthalpy of the phase transitions, were measured with the differential scanning calorimetry technique. These SOA components exhibit relatively high melting temperatures from 364.32 K for cis-pinic acid to 440.68 K for cis-norpinic acid. The enthalpies of fusion vary from 14.75 kJ·mol-1 for cis-norpinic acid to 30.35 kJ·mol-1 for cis-pinonic acid. The solubility in water was determined with the dynamic method (solid-liquid phase equilibria method), and then experimental results were interpreted and correlated using three different mathematical models: Wilson, non-random two-liquid model, and universal quasichemical equations. The results of the correlation indicate that the Wilson equation appears to work the best for all investigated compounds, giving rise to the lowest value of a standard deviation. cis-Norpinic acid and cis-pinic acid (dicarboxylic acids) show better solubility in the aqueous solution than cis-norpinonic acid and cis-pinonic acid (monocarboxylic acids), which affect the multiphase chemistry of α-pinene SOA processes. For cis-pinonic acid and cis-norpinonic acid, also pH-profile solubility was determined. The intrinsic solubility (S0) for cis-norpinonic acid was measured to be 0.05 mmol·dm-3, while for cis-pinonic acid, it was found to be 0.043 mmol·dm-3. The acidity constants (pKa) at 298 and 310 K using the Bates-Schwarzenbach spectrophotometric method were determined. The pKa values at 298.15 K for cis-norpinonic acid and cis-pinonic acid were found to be 4.56 and 5.19, respectively, whereas at 310.15 K, pKa values were found to be -4.76 and 5.25, respectively.

In this study, we present a complete description of the addition of a model nucleophile to the nitroaromatic ring in positions occupied either by hydrogen (the first step of the SNAr-H reaction) or a leaving group (SNAr-X reaction) using theoretical parameters including aromaticity (HOMA), electrophilicity and nucleophilicity indices. It was shown both experimentally and by our calculations, including kinetic isotope effect modeling, that the addition of a nucleophile to the electron-deficient aromatic ring is the rate limiting step of both SNAr-X and SNAr-H reactions when the fast transformation of &sigma, H-adduct into the products is possible due to the specific reaction conditions, so this is the most important step of the entire reaction. The results described in this paper are helpful for better understanding of the subtle factors controlling the reaction direction and rate.

Isoprene (C5H8) is the main non-methane hydrocarbon emitted into the global atmosphere. Despite intense research, atmospheric transformations of isoprene leading to secondary organic aerosol (SOA) are still not fully understood, including its multiphase chemical reactions. Herein, we report on the detailed structural characterization of atmospherically relevant isoprenederived organosulfates (OSs) with a molecular weight (MW) of 212 (C5H8SO7), which are abundantly present in both ambient fine aerosol (PM2.5) and laboratory-generated isoprene SOA. The results obtained from smog chamber-generated isoprene SOA and aqueous-phase laboratory experiments coupled to the S(IV)-autooxidation chemistry of isoprene, 3-methyl-2(5H)-furanone, and 4-methyl-2(5H)-furanone, allowed us for the first time to fully elucidate the isomeric structures of the MW 212 OSs. By applying liquid chromatography interfaced to electrospray ionization high-resolution mass spectrometry, we firmly confirmed six positional isomers of the MW 212 OSs in PM2.5 collected from different sites in Europe and the United States. Our results also show that despite the low solubility of isoprene in water, aqueous-phase or multiphase chemistry can play an important role in the formation of OSs from isoprene. Possible formation mechanisms for the MW 212 OSs are also tentatively proposed.

Bimolecular reaction rate coefficients (kOH) for reaction of hydroxyl radicals (OH) with adipic, pimelic, suberic, azelaic, sebacic and cis-pinonic acids were measured in aqueous phase for the neutral (pH = 2) and completely deprotonated (pH = 9) forms of the acids listed. Reactions were carried out in bulk solution between 283 and 318 K. Camphoric acid was used as a reference compound for measuring kOH values using a relative rate method, and with hydrogen peroxide (H2O2) as a photochemical source of OH. Concentrations of the reactants were monitored with liquid chromatography coupled with electrospray tandem mass spectrometry (LC-ESI/MS2). The kOH values measured were between 1 and 8 × 10-9 M-1s-1; only adipic and pimelic acids showed a significant pH-dependence to their OH reactivity. The kinetic data acquired and the data reported in the literature for camphoric, glutaric and succinic acids were used to optimize new structure-activity relationship (SAR) parameters. The SAR developed here allowed accurate prediction of kOH values for aliphatic carboxylic acids in the temperature range between 283 and 318 K. The accuracy of the developed SAR was evaluated against the experimental kOH values measured in this work and obtained from the literature data. Moreover, this work is the first to accurately predict the temperature-dependent kOH values for carboxylic acids.

International journal of molecular sciences 22(15), 8033 (2021). doi:10.3390/ijms22158033 special issue: "Physical Chemistry and Chemical Physics", Published by Molecular Diversity Preservation International, Basel

The mechanism of intramolecular gas-phase reactions of N-(2-X-5-nitrophenyl)-N-methylacetamide carbanions (X=H, F, Cl) has been studied using negative ion electrospray mass spectrometry ((-)ESI-MS) technique and modelled computationally. It was proven that all three anions form cyclic σ(H) adducts, which undergo elimination of water. In the case of X=F, formation of the σ(F) adduct, leading to SN Ar reaction, was a competing process. This is the first proof that also in the gas phase formation of σ(H) adduct proceeds faster than σ(X) adduct and only when X=F, rates of these two processes are comparable. The experimental results are in full agreement with quantum chemical calculations.

Gas-phase proton affinities (PA) of the carboxylate anions are very important parameters for gas-phase as well as condensed-phase reaction studies. Comparison of the PA values with pKa values of the respective carboxylic acids in solution gives information about the solvation effects on the acidity of these compounds. In the present work we have measured the PA values of about 65 aromatic acids using Cooks’ kinetic method. About 30 of these acids have been investigated previously by other researchers and served as the reference compounds in our work. The results of MS measurements were evaluated using three methods differing by the level of simplification. We found that for the series of the studied acids there were no significant differences between these methods, so even the simplest one, which does not take into account entropy effects, can be used. The case of the only exception: o-hydroxybenzoic (salicylic) acid is discussed. It was also found that the kinetic method can be used for acids whose anions undergo further fragmentation under experimental conditions.

Reaction of N-aryl-2-nitrosoanilines with alkyl aryl­idenecyanoacetates in the presence of Et3N in MeCN leads to substituted 1,2,3,4-tetrahydroquinoxaline derivatives in reasonable yields. The reaction comprises nucleophilic addition of the nitrosoaniline to the Michael acceptor followed by cyclization involving the nitroso group. Since the reactive nitrogen groups in N-aryl-2-­nitrosoanilines are of opposite character the reaction is regioselective and additionally it was found to be diastereoselective.

Methyl thiocyanate, like other organic thiocyanates, is a molecule with many electrophilic reactive sites and it has many synthetic applications. For better understanding of the intrinsic reactivity of alkyl thiocyanates against nucleophiles it was important to study gas-phase reactions of methyl thiocyanate with carbanions differing by structure and proton affinity values.All experiments were performed using a modified API 365 triple quadrupole mass spectrometer equipped with a TurboIonSpray electrospray ionization (ESI) source. Carbanions were generated in the ESI source by decarboxylation of the respective carboxylic acid anions. Methyl thiocyanate was delivered as a vapor with nitrogen used as a collision gas to the collision cell where the reactions take place.Mass spectra recorded for the gas-phase reactions of five aliphatic carbanions with methyl thiocyanate showed a variety of product ions formed via different reaction mechanisms, depending on the structure and proton affinity of the carbanion. The pathways considered are: SN 2 nucleophilic substitution, cyanophilic reaction, thiophilic reaction and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory (DFT) calculations.Our preliminary experiments showed that mass spectrometry together with quantum chemical calculations is a good tool for studying gas-phase reactions of alkyl thiocyanates with carbanions. In the gas phase all four theoretically possible products can be observed and their formation can be rationalized by the results of the modelling of the reaction energy profiles. Copyright © 2016 John WileySons, Ltd.

Quinoline derivatives are interesting objects to study internal reorganizations due to the observed excited-state-induced intramolecular proton transfer (ESIPT). Here, we report on computations for selected 12 quinoline derivatives possessing three kinds of intramolecular hydrogen bonds. Density functional theory was employed for the current investigations. The metric and electronic structure simulations were performed for the ground state and first excited singlet and triplet states. The computed potential energy profiles do not show a spontaneous proton transfer in the ground state, whereas excited states exhibit this phenomenon. Atoms in Molecules (AIM) theory was applied to study the nature of hydrogen bonding, whereas Harmonic Oscillator Model of aromaticity index (HOMA) provided data of aromaticity evolution as a derivative of the bridge proton position. The AIM-based topological analysis confirmed the presence of the intramolecular hydrogen bonding. In addition, using the theory, we were able to provide a quantitative illustration of bonding transformation: from covalent to the hydrogen. On the basis of HOMA analysis, we showed that the aromaticity of both rings is dependent on the location of the bridge proton. Further, the computed results were compared with experimental data available. Finally, ESIPT occurrence was compared for the three investigated kinds of hydrogen bridges, and competition between two bridges in one molecule was studied.

Sequential nucleophilic addition of nitroaniline to alkyl arylidenecyanoacetates and intramolecular cyclization provides tetrahydroquinoxaline derivatives with excellent regio- and diastereoselectivity.

Car–Parrinello molecular dynamics simulations were carried out for 8-hydroxyquinoline N-oxide (1) and 2-carboxyquinoline N-oxide (2) in vacuo and in the solid state. The first-principle approach was employed to intramolecular hydrogen bond features present in the studied quinoline N-oxides. Grimme’s dispersion correction was employed throughout the study. Special attention was devoted to the solid-state computations knowing that in the molecular crystals, strong and weak interactions are responsible for spatial organization and molecular properties of molecules. On the basis of Car–Parrinello molecular dynamics, it was possible to reproduce the hydrogen bond dynamics as well as to investigate the vibrational features on the basis of Fourier transform of the atomic velocity autocorrelation function. The free energy surfaces for proton motion were reproduced by unconstrained CPMD runs as well as by metadynamics. Larger flexibility of the bridge proton in 2 was noticed. The computations are verified by experimental X-ray and IR data available.