Carbocations are key intermediates in many important organic reactions. The remarkable effect of the solvent composition on the kinetic parameters of the carbocation decay and product composition was found in the photolysis of 1,2,2,3-tetramethyl-1,2-dihydroquinoline () in 2,2,2-trifluoroethanol (TFE)–H₂O mixtures. The rate constant of the intermediate carbocation decay has a maximum, and the activation energy is minimal in the TFE–H₂O mixture 3 : 7 (v/v). In the steady-state photolysis, products of oligomerization of with n up to 8 and their adducts with TFE and H₂O were identified at this solvent composition. The results were rationalized in terms of TFE clustering in aqueous mixtures, with the maximum of cluster formation at 30 vol % TFE. The clusters form a pseudo-phase, in which the molecules of are concentrated and the carbocations are generated. TFE, H₂O and compete in the combination reaction with the photogenerated carbocation to afford the products. This effect was not observed for 1,2,2,4-tetramethyl-1,2-dihydroquinoline (), the isomer of , due to steric hindrance at C(4) carbon atom of the heterocycle, the active site of the intermediate carbocation, which makes impossible for the carbocation from to react further with . Thus, the kinetic parameters and the product composition in the photolysis of in TFE–H₂O mixtures reflect the changes in the microstructure of the binary solvent. Copyright © 2013 John Wiley & Sons, Ltd.

Herein we use small molecule models of stimuli-induced degradable/depolymerizable polymers to demonstrate that less aromatic releasing units provide faster rates of azaquinone methide-mediated release of benzylic phenols (a surrogate for a group released in a polymer) than highly aromatic releasing units. Copyright © 2013 John Wiley & Sons, Ltd.

7-R-9-ethyl-6,9-dihydro-6-oxo-[1,2,5]selenadiazolo[3,4-h]quinolines (R = H, COOC₂H₅, COOCH₃, COOH and COCH₃, ) and 6-ethyl-6,9-dihydro-9-oxo-[1,2,5]selenadiazolo[3,4-f]quinoline () were characterized by UV/vis, FT-IR and fluorescence spectroscopy. The electronic absorption spectra of the derivatives and in the aprotic solvents dimethylsulfoxide (DMSO) and acetonitrile (ACN) reveal low-energy absorption maxima with λ_max > 400 > nm, shifted hypsochromically in water. In DMSO, N-ethyl selenadiazoloquinolones behave as strong fluorescent agents (λ_em ≥ 550 nm) with the exception of the carboxylic acid derivative which shows only poor emission. Photoinduced reactions of N-ethyl selenadiazoloquinolones were investigated by means of electron paramagnetic resonance (EPR) spectroscopy. Photoexcitation of N-ethyl selenadiazoloquinolones in aerated DMSO with either 385 nm or 400 nm wavelengths, monitored by EPR spin trapping technique, results in the generation of superoxide radical anions; under an inert atmosphere, the generation of methyl radicals originating from the solvent predominates. Upon exposure at either 365 nm, 385 nm or 400 nm, aerated ACN solutions of selenadiazoloquinolones in the presence of sterically hindered amines produce nitroxide radicals via a reaction with photogenerated singlet oxygen. The 7-substituted derivatives of 9-ethyl-6,9-dihydro-6-oxo-[1,2,5]selenadiazolo[3,4-h]quinoline behave as photosensitizers activating molecular oxygen upon photoexcitation and possess the sufficient photochemical stability under the given experimental conditions. The cytotoxic effects of non-photoactivated and UVA photoactivated N-ethyl substituted selenadiazoloquinolones on cancer (human HeLa and murine L1210) and non-cancer (NIH-3T3) cell lines were monitored by the MTT test. The derivative demonstrates the highest cytotoxic/photocytotoxic activity on the neoplastic cell lines. Copyright © 2013 John Wiley & Sons, Ltd.

We report computations of excitation energies, magnetizabilities, and current strengths for the dianion, tetraanion, and hexaanion of the previously introduced altan–corannulene, a molecule designed to hold a strong paratropic current. None of these ions has a fully diatropic or paratropic pattern: dianion and tetraanion both have a paratropic/diatropic/diatropic pattern, whereas the hexaanion has a diatropic/paratropic/diatropic pattern, which is the ‘mirror-image’ of that of the neutral species. The patterns have been interpreted according to the ipsocentric formulation of the current density. Magnetizability and excitation energy suggest that the hexaanion should be an aromatic molecule. The next homologue of altan-corannulene^6-, altan–altan–corannulene^6-, has also been studied. Its large diamagnetizability has been effectively used to model the magnetic response of C₈₀^6- cages. Copyright © 2013 John Wiley & Sons, Ltd.

The mechanism of sulfurization of substituted triphenylphosphines with 4-(3- and 4-substituted)-1,2,4-dithiazolidine-3,5-diones in acetonitrile, dichloromethane, tetrahydrofuran and toluene at 25 °C was studied. The reaction pathway involves rate-limiting initial nucleophilic attack of the phosphorus at sulfur followed by fast decomposition of the phosphonium intermediate to the corresponding phosphine sulfide, phenylisocyanate and carbonylsulfide. From the Hammett correlations and from the solvent dependency, it was concluded that the transition-state structure is very polar and resembles the zwitter-ionic intermediate. The extent of P–S bond formation and S–S bond cleavage is very similar in the solvents series, but the latter gradually decreases with the decreasing polarity of the solvent. Copyright © 2013 John Wiley & Sons, Ltd.

We present a review of the methods most frequently used for the synthesis of fullerenes and the changes that these methods have experienced since 1985 when Kroto and co-workers discovered C₆₀. We also analyze the most important models that explain the mechanism of the formation of fullerenes in carbon soot, as well as the new methodologies that lead to the rational chemical synthesis of fullerenes and of fullerene fragments as precursors. Copyright © 2013 John Wiley & Sons, Ltd.

Preferential cross-coupling of differently N-substituted amides of 3-hydroxy-2-naphthoic acids 1 and 2 catalyzed by Cu(OH)Cl•TMEDA was observed. The reaction mechanism was investigated using mass spectrometry tools. It was shown that the complexation properties of the N-substituent significantly influence the properties of the corresponding copper complexes of the deprotonated compounds ([(1-H)Cu(TMEDA)]⁺ and [(2-H)Cu(TMEDA)]⁺). Analysis of the fragmentation patterns of the copper complexes revealed that while the former is prone to the one electron oxidation of (1-H)ˉ, the latter has a larger binding energy between (2-H)ˉ and copper(II). Interplay between the abundance of the copper complexes and their reactivities explains the preferential cross-coupling. The results are further supported by exploratory density functional theory calculations. Copyright © 2013 John Wiley & Sons, Ltd.

Examining the structures presented by Loschmidt in 1861 shows that he portrayed organic structures in a visually appealing way, but the structures do not support several claims and accolades of Loschmidt's modern-day champions. There is serious doubt that Loschmidt viewed benzene as a planar cyclic array of six carbon atoms; he did not understand positional isomerism of benzene derivatives or the essence of geometric isomerism. He did not recognize that carbons of the C₆ nucleus could only be singly bonded to a substituent. Concerning his “prediction” of cyclopropane, Loschmidt may have been the first to consider a “circular” array of three atoms; this achievement must be viewed in the light of similar predictions for a cyclic dinitrogen oxide, tetracyclohexane, heptacyclononane, and a [1,1]-metacyclophane. His structures worked well for strings of sp²-hybridized carbons or for molecules with chains of tri-substituted carbons. Loschmidt did not differentiate between the bond lengths of double and triple bonds, as claimed. Copyright © 2013 John Wiley & Sons, Ltd.

The adducts of copper(II) chloride complexes with organic radicals may be intermediates in reactions of halohydrocarbons proceeding via radical mechanism and in catalyzed by chlorocuprates. In this paper, the structure and reactivity of chloroorganocuprates with general formula [CuCl_nCH₃]²⁻ⁿ (n = 0–4) were studied at density functional theory (DFT) level of theory. The comparison of geometric and electronic structures of chloroorganocuprates and corresponding copper(II) chloride complexes with the same number of chlorine atoms indicates the higher Cu oxidation state in [CuCl_nCH₃]²⁻ⁿ. The Natural Bonding Orbital analysis confirms the formation of covalent σ-Cu–C bond in these complexes. The analysis of the PES of the system CuCl₄²⁻–CH₃^• indentifies two local minima, corresponding to CuCH₃Cl₄²⁻ and weak complex CuCl₃²⁻···CH₃Cl, as well as transition state between them. The calculations evidence the spontaneous character of copper ion reduction with formation of halohydrocarbon by chlorine atom detachment from CuCl₄²⁻ with high energetic effect. Copyright © 2013 John Wiley & Sons, Ltd.

A set of N₊ nucleophilicity parameters (N₊″) are reported for amines, carbanions and various other nucleophiles in methanol at 20 °C. N₊″ = N″ +2.63, where N″ refers to logarithms of second-order rate constants for reactions of the dimethylamino- benzhydrylium cation (dma)₂CH⁺ with various nucleophiles in any solvent at 20 °C; as for other N₊ parameters, N₊″ = 4.75 for hydroxide in water. Logarithms of second-order rate constants (log k) are correlated by a hybrid of Swain-Scott and Ritchie (SSR) equations: log k = s_E × N₊″ + c, where s_E is the response of the electrophile to changes in N₊″ and c is a residual intercept term. Satisfactory results are obtained for some nucleophilic reactions at sp³ carbon, including S-methyldibenzothiophenium triflate (reference substrate for the N_T scale of solvent nucleophilicity), a methoxymethyl derivative and methyl p-nitrobenzenesulfonate. Less satisfactory results are obtained for acetyl chloride. The results extend the scope of the hybrid SSR equation to nucleophilic substitutions and provide additional insights into the factors influencing s_E. A previously published equation containing two response (s) parameters is shown to be less reliable, and an alternative is investigated. Copyright © 2012 John Wiley & Sons, Ltd.

Dihydrogen bond (DHB) and X–H…σ interaction are discussed and compared here. Both interactions possess numerous characteristics of the hydrogen bond (HB). The Natural Bond Orbitals method results show that σ → σ* is the most important interaction connected with the electron charge transfer from the Lewis base to the Lewis acid for the DHB as well as for the X–H…σ HB. However, there are distinct differences between these interactions, and this is evident from the analysis based on the Quantum Theory of Atoms in Molecules as well as from the decomposition of the energy of interaction. The X–H…π interaction is also discussed here since it possesses few characteristics typical for the X–H…σ interaction and not for the DHB. Copyright © 2013 John Wiley & Sons, Ltd.

For conventional organic substituents, an almost linear relationship can be established between the para Hammett constants in aqueous solutions and chemical shifts or natural population analysis charges (NPA charges). Based on these correlations, the Hammett constants of six synthesized ionic-pair substituents were estimated via the chemical shifts, which were well in agreement with the results calculated by NPA charges. The para Hammett constants of 89 different ionic-pair substituents (77 anion-cationic and 12 cation-anionic) were therefore calculated in the gas phase based on the density functional theory method. The results show that both the anion-cationic and cation-anionic substituents are electron-withdrawing groups and the different cation–anion combinations could tune the Hammett constants of the ionic-pair substituents in a range from 0.03 to 0.77. Copyright © 2013 John Wiley & Sons, Ltd.

Using Fourier Transform Ion Cyclotron Resonance Spectrometry, we have determined the gas-phase acidities (GA) of 1-phenylethanol, diphenylmethanol and triphenylmethanol. Combining these results with the available experimental data for other alcohols, we obtained three sets of experimental acidities for the families (CH₃)_nC–OH, (CF₃)_nC–OH and Ph_nC–OH (n = 1–3) as well for some other α-substituted alcohols combining these substituents. GA values for these alcohols were studied at the B3LYP/6-311 + G(d,p), MP2/6-311 + G(d,p), G3(MP2) and G3 levels. This allowed the prediction of a number of GA values for other alcohols. We also developed an empirical method for the estimation of these magnitudes and used it to predict the cases wherein simple additivity of substituent effects would break down. Copyright © 2013 John Wiley & Sons, Ltd.

Molecular mutagens and carcinogens are structures which carry chemical and electronic properties that disturb and interact with the genomic machinery. Principally, a rule of thumb for carcinogens is that carcinogens are expected to introduce covalent irreversible bonding to one or several types of DNA bases, causing errors in the reading frame for the polymerases. 8-methoxy-6-nitrophenanthro[3,4-d][1,3]dioxole-5-carboxylic acid, better known as Aristolochic acid (AA1) is a recognized carcinogen which causes urotherial cancer and is found in certain plants. Its structure is particularly interesting given that it is closely related to phenanthrene in its polycyclic arrangement, and has four functional groups, a carboxyl-, a nitro-, a methoxy- and a dioxolane group. In this work, the structure of AA1 has been resolved at the MPWPW91 density functional theory method in combination with Aug-cc-pVDZ basis sets. A geometry analysis shows that in AA1 the carboxyl group's torsion is caused by steric strain from the nitro group, which elevates the molecular plane of the first phenanthrene ring with 0.1Å. The wavefunction analysis of AA1 shows that the ring deformation enhances a double π-bond localization in the first ring, adjacent to the dioxalane group, and results in a decrease of ring aromaticity and induces a potentially frozen resonance. Intermolecular and intramolecular interactions were characterized by atoms in molecules and reduced density gradient analysis. This study brings novel information on the geometry and electronic structure of AA1, which are important for the further knowledge of its transformation in vivo and in situ. Copyright © 2013 John Wiley & Sons, Ltd.

Gas-phase heats of formation (HOF), solid-phase HOF, detonation properties, electronic structure and thermal stability for a series of polynitro pyrazine derivatives containing three heterocycles have been investigated using density functional theory. It is found that the nitro group is an efficient tool to improve HOF of pyrazine derivatives. Furthermore, detonation velocities and detonation pressures of these compounds are evaluated using empirical Kamlet–Jacobs equations. As a result, it indicates that the nitro group is useful to enhance detonation properties. Detonation velocities of five compounds are 9.67, 9.20, 9.74, 9.76 and 9.87 km/s, respectively, which are significantly larger than that of HMX (9.10 km/s). Bond dissociation energy is also performed to investigate their thermal stability, showing that thermal stability of these compounds is little affected by nitro groups or the position of substituent groups. Considering solid-phase HOF, detonation properties and thermal stability, some of pyrazine derivatives can be potential high energy density materials. Copyright © 2013 John Wiley & Sons, Ltd.

Through-conjugation for a wide range of 1,8-diamino-4,5-dinitronaphthalenes (N-acylated, N-alkylated, N,N′-bridged, N-heterocyclic, and N-deprotonated compounds) was for the first time quantified in solution by means of ultraviolet–visible and proton nuclear magnetic resonance spectroscopy and compared with that of the simpler naphthalene and benzene push-pull systems. Surprisingly, an extent of conjugation in 1,8-diamino-4-nitro- and 1,8-diamino-4,5-dinitronaphthalenes measured in dimethyl sulfoxide is commensurable. On the whole, the repulsive peri-interactions between the amino groups in systems with N-alkylated and N-deprotonated amino groups are more favorable for an effective D-π-A charge transfer than in N,N′-bridged compounds (perimidines, 2,3-dihydroperimidines and perimidin-2-ones). The best electron donors from peri-positions are pyrrolidin-1-yl and methylamido groups. The conclusions obtained from solution studies were deepened by solid- state X-ray experiments for a number of push–pull naphthalenes, including 6,7-dinitroperimidine N-anion and two representatives of 4,5-diaminonaphthalene-1,8-dicarbaldehydes. In particular, they helped to trace changes in the bond order redistribution and twisting of the naphthalene core. The latter reaches a record value of 27° for 4,5-dinitro-1,8-di(pyrrolidin-1-yl)naphthalene. Copyright © 2013 John Wiley & Sons, Ltd.

The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (alkyl: methyl, ethyl) and (ethoxymethylidene)malononitrile with substituted hydrazines and anilines R¹–NH₂ (R¹: (CH₃)₂N, CH₃NH, NH₂, C₆H₅NH, CH₃CONH, 4-CH₃C₆H₄SO₂NH, 3- and 4-X-C₆H₄; X: H, 4-Br, 4-CH₃, 4-CH₃O, 3-Cl) were studied at 25 °C in methanol. It was found that the reactions with all hydrazines (the only exception was the reaction of (ethoxymethylidene)malononitrile with N,N-dimethylhydrazine) showed overall second-order kinetics and k_obs were linearly dependent on the hydrazine concentration which is consistent with the rate-limiting attack of the hydrazine on the double bond of the substrate. Corresponding Brønsted plots are linear (without deviating N-methyl and N,N-dimethylhydrazine), and their slopes (β_Nuc) gradually increase from 0.59 to 0.71 which reflects gradually increasing order of the C–N bond formed in the transition state. The deviation of both methylated hydrazines is probably caused by the different site of nucleophilicity/basicity in these compounds (tertiary/secondary vs. primary nitrogen). A somewhat different situation was observed with the anilines (and once with N,N-dimethylhydrazine) where parabolic dependences of the kinetics gradually changing to linear dependences as the concentration of nucleophile/base increases. The second-order term in the nucleophile indicates the presence of a steady-state intermediate - most probably T^±. Brønsted and Hammett plots gave β_Nuc = 1.08 and ρ = −3.7 which is consistent with a late transition state whose structure resembles T^±. Copyright © 2013 John Wiley & Sons, Ltd.

The mechanisms of the [2 + 2 + 2] cycloaddition reaction of three ethyne molecules were studied by ab initio molecular orbital and density functional methods. The transition states range from that of the concerted mechanism with D_3h symmetry to that of the stepwise mechanism with C₂ symmetry. The transition state structure and the activation energy depend on the basis set and computational method employed in the analysis. The activation energy barrier was determined to be in the range of 36–44 kcal/mol. The activation energy determined by various methods corresponds to the interaction energy, which is related to the electron correlation energy. The best estimation of the activation energy barrier is 41.6 kcal/mol, achieved from the relation between the interaction energy and the activation energy. Copyright © 2013 John Wiley & Sons, Ltd.