On the basis of a quantum chemical analysis of potential energy surfaces (PESs) of intermediate radical anions (RAs), we give a theoretical interpretation for the emergence of unusual products of the reductive deflourination of perfluorinated xylenes under the action of Zn(Cu)-DMF-H2O, observed by V.I. Krasnov et al in 1997: in the case of ortho- and meta-isomers, the fluorine atoms of the aromatic ring are replaced by hydrogen atoms, while the fluorine atoms of trifluoromethyl groups are retained. Using a hybrid model combining the supermolecular approach with the polarizable continuum model to consider the effects of solvation, we performed DFT calculations of the sections of the PESs mentioned along the coordinates of fluoride ion elimination from different positions of the RAs. The calculation results show that an outcome of the competition between the aryl and alkyl C-F bonds to be broken is determined by a ratio of the corresponding activation barriers.

A stepwise qualitative consideration of the reduction in symmetry for the highly symmetrical "right sandwich" and "twisted sandwich" structures of the stacked benzene dimer caused by the pseudo-Jahn-Teller effect made it possible to construct a scheme of the potential energy surface (PES) of this dimer. Thirty-six equivalent structures of minimum energy are ordered on this extremely flat surface, transforming into each other in an almost barrier-free manner. There are two kinds of these transformations, both of which are pseudorotation. The transformation pathways inherent in this neutral dimer are also characteristic of its radical cation (RC). Structural transformations of the RC are inextricably linked with changes in its electronic state since its stationary structures relate to different electronic states. (C6H6)2+˙ exists in the form of two orbital isomers, each of which "pseudorotates" on its own area of the PES. During the pseudorotation, the SOMO distribution on the fragments of (C6H6)2+˙ changes, which is identical to what occurs during the pseudorotation of the Jahn-Teller benzene RC. These areas are connected by pairwise interconversions of their minimum energy structures. The interconversion of the orbital isomers is a bypassing of conical intersections between corresponding electronic states, which occurs through a synchronized pseudorotation of the fragments. The conclusions of the qualitative consideration and the results of quantum chemical calculations of various levels performed for (C6H6)2+˙ are in full agreement with each other. The revealed features of the structure of the PES of the two reference systems in studying the intermolecular and ion-molecule interactions are the basis for considering their more complex analogs, primarily their less symmetrical ones.

Using the method of time-resolved magnetic field effect in radiation-induced fluorescence, primary radical cations (RCs) in irradiated poly(isobutylene) (PIB) have been detected for the first time. A comparison of experimental results with the data of quantum chemical calculations suggests that the initial geometry of the ionized fragment of the PIB molecule is close to the geometry of the neutral polymer in the trans-gauche-trans-gauche conformation. The spin density of the RC in this geometry is delocalized over more than 10 polymer units, and the width of the RC's EPR spectrum is about Delta H-pp approximate to 1.3 mT. At a temperature of 273 K and lower, the lifetime of the primary RCs with the delocalized spin density exceeds 10 ns. The structural relaxation of the RCs results in the spin density localization on a single C-C bond, which is extended to nearly 0.2 nm, and in the increase in the EPR spectrum width to Delta H-pp approximate to 2.4 mT. It looks likely that this intramolecular structural relaxation is coupled strongly with those types of molecular motions that determine the process of dielectric beta-relaxation in the polymer.

The mechanism of the reductive dehalogenation of 3-chloro-2,4,5,6-tetrafluoropyridine has been considered in terms of quantum-chemical analysis of the potential energy surface (PES) for its daughter radical anion (RA). We analyzed PES sections along the coordinates of the RA fragmentation through the loss of a halide ion. Based on DFT calculations, a model has been built that included the solvent reorganization during the RA decomposition. The model enabled us to describe the change of the RA decay channel with an increase in solvent polarity which was found by V.P. Krasnov and V.E. Platonov, 2000. The change is due to a difference in the fine mechanisms of C-F and C-Cl bond cleavage.

Magnetic resonance characteristics of carriers of both electron spin and electric charge (polarons) in conjugated polymers are required for a deeper understanding of properties of these semiconducting materials. In poly(3-hexyl-thiophene), P3HT, which is an important material for photovoltaic applications, such information is available only for positive polarons, which are readily generated in the presence of electron acceptors via photoinduced processes. Influence of an external magnetic field on X-ray-induced delayed fluorescence from undoped P3HT and its solutions allowed us to visualize the spin interactions in the primary polaron pairs and to estimate the g-tensor components (g⊥ ≈ 2.0023, g|| ≈ 2.008) for the negative charge carriers in P3HT molecules. There is evidence that in neat regioregular P3HT, the g-tensor anisotropy for the polarons, migrating along polymer chains, is averaged partially because of irregularities in the polymer structure.

for the first time the question is raised concerning the effect of ion-molecular associations on the structural flexibility of radical ions of aromatic compounds with respect to pseudorotation. It is shown within the DFT method that the complex structure of the potential energy surface and structural flexibility of the Jahn-Teller benzene cation are preserved during the formation of complexes with a hydrogen cyanide or acetonitrile molecule. The pseudorotation barrier of the radical cation in considered complexes depends on the relative orientation of particles and varies from 0.1 kcal/mol to ∼2 kcal/mol.

While there is a body of experimental data concerning dimers formed by an aromatic molecule and its radical cation, information on the corresponding dimer radical anions (DRAs) is scarce. In this work, evidence for the formation of the DRAs of decafluorobiphenyl and 4-aminononafluorobiphenyl has been obtained by the optically detected electron paramagnetic resonance and the time-resolved magnetic field effect techniques. Theoretical investigation (DFT B3LYP-D3/6-31+G*) of these DRAs and the DRAs of octafluoronaphtalene and 1,2,4,5-tetrafluorobenzene previously detected by Werst has been undertaken to gain greater insight into the structure of the polyfluoroarene DRAs. Without substituents different from a fluorine atom, an extra electron is evenly delocalized over two fragments; the bonding interaction is π stacking. On the potential energy surfaces (PES), there are two minima of nearly equal energy corresponding to the structures of perfect and parallel displaced sandwiches. Such a PES structure is due to a conical intersection between two electronic states of different symmetry. The DRA of 4-aminononafluorobiphenyl is an ion-molecular associate stabilized by electrostatic interactions involving NH2 groups. The complex cyclic structure of the PES of this DRA suits the successive electron transfers between the dimer fragments. The calculated hyperfine coupling constants averaged over the PES minima agree well with the experimental ones.

The method of time resolved magnetic field effects in the recombination fluorescence of spin-correlated radical ion pairs is used to detect for the first time the perfluorobenzocyclobutene radical anion. The quantum chemical analysis of the potential energy surface testifies that the particle is structurally flexible with respect to the pseudo-rotation coordinate. The calculated values of hyperfine interaction constants averaged over global minima are close to those estimated from the experimental data of time resolved magnetic field effects.

Впервые затронут вопрос о влиянии ион-молекулярной ассоциации на свойственную ион-радикалам ароматических соединений структурную нежесткость по отношению к псевдовращению. В рамках метода DFT показано, что сложное строение поверхности потенциальной энергии и структурная нежесткость ян-теллеровского катиона бензола сохраняются при образовании комплексов с молекулой циановодорода или ацетонитрила. Высота барьера псевдовращения катион-радикала в рассмотренных комплексах зависит от взаимной ориентации частиц, находясь в диапазоне от 0.1 ккал/моль до ~2 ккал/моль.

Experiments show that 1,1'-bi-2-naphthol (BINOL) undergoes facile C1-C1' bond cleavage under action of triflic acid at temperatures above 0 °C to give mainly 2-naphthol along with oligomeric material. CASSCF and MRMP//CASSCF computations have demonstrated unambiguously that this unusual mode of scission of the biaryl bond can occur in the C1,C1'-diprotonated form of BINOL via a mechanism involving homolytic cleavage prompted by the intramolecular electrostatic repulsion. These findings also provide insights into the mechanism of a comparatively easy thermal cleavage of BINOL, implying the intermediacy of its neutral diketo form.

Методом времяразрешенного магнитного эффекта в рекомбинационной флуоресценции спин-коррелированных ион-радикальных пар впервые зафиксирован анион-радикал перфторбензоциклобутена. На основе квантово-химического анализа поверхности потенциальной энергии сделан вывод о структурной нежесткости данной частицы по отношению к координате псевдовращения. Рассчитанные значения констант сверхтонкого взаимодействия, усредненные по глобальным минимумам, близки к оцененным из экспериментальных данных времяразрешенного магнитного эффекта.

The effect of an external magnetic field on the radiation-induced fluorescence of tricosane (n-C23H48), doped with luminophore, was studied on the nanosecond timescale. It was found that the characteristic frequency of quantum beats caused by the difference between the Zeeman interactions of dopant radical anions and tricosane radical cations increased substantially upon transition from the liquid to the crystal phase. Experimental data were in agreement with both the quantum-chemical calculations and theoretical spin evolution simulations, assuming that hyperfine couplings and transverse components of the tricosane radical cation g-tensor were averaged out by degenerate positive charge transfer in the tricosane crystal.

We have studied the interaction of polyfluorinated (in the benzene moiety) 2-chloroquinolines with liquid and aqueous ammonia as an approach to the synthesis of halogen-containing aminoquinolines. 5,7-Difluoro-, 5,6,8-trifluoro-, and 5,7,8-trifluoro-2-chloroquinolines mostly form products of substitution of the Cl atom, whereas 5,7-difluoro-2,6-dichloroquinoline, 5,6,7,8-tetrafluoro-, and 6,7-difluoro-2-chloroquinolines yield products of substitution of an F atom at various positions. The replacement of liquid ammonia with aqueous causes an increase in the proportion of the products of aminodechlorination relative to the products of aminodefluorination. For 2-chloro-6,8-difluoroquinoline this replacement leads to 2-amino-6,8-difluoroquinoline as the main product instead of the 8-amino-derivative. Activation energy values estimated by DFT calculations for the reactions in question agree with the reaction regioselectivity observed experimentally.

DFT calculations were used to study the potential energy surfaces (PESes) of a full series of fluorinated benzoate radical anions (RAs). The sections of PESes along the C-F bond cleavage coordinates in polar media were built, and the transition states for RA fragmentation with fluoride anion elimination were located. The estimated reaction barrier heights let us interpret the experimental regularities of the RA decay including the process regioselectivity.The fragmentation mechanism was shown to depend on the position of the leaving fluorine atom. When defluorination occurs at an ortho- or meta- position to the CO2- group, the reaction coordinate involves pseudorotation as a way for odd electron density transfer to the breaking C-F bond.Additional gas phase calculations were performed to confirm the pseudorotational architecture of the PESes of polyfluorinated benzoate RAs. The results obtained clearly demonstrated that the multihole PES structure gives rise to the multichannel mechanism of RA cleavage. (C) 2016 Elsevier B.V. All rights reserved.

The review proposed summarizes the results of investigations on the adiabatic potential energy surfaces (PESes) for the radical ions of some derivatives of highly symmetric organic molecules such as benzene and cyclohexane. The results obtained show that the main feature of the PESes of highly symmetric Jahn–Teller ions, namely conical intersection, may persist for their low-symmetric derivatives. Hence, their PESes have a pseudorotational shape resulting from the intersection avoidance. A distinctive feature of radical anions of fluorine containing aromatic compounds is the planar structure disturbance due to the vibronic coupling of the ground π and low-lying excited σ states. The data on the PES structure including the positions and relative energies of its extrema, curvature in their vicinity, and stationary point interrelations provide the foundation for understanding the spectral properties and reactivity of radical ionic species. Examples of applying the PES study results to experimental data interpretation are given. © 2015 Wiley Periodicals, Inc.

A concise noncatalytic synthetic approach to 2‐ and 3‐substituted 4,4′‐dicyanobiphenyls by applying terephthalonitrile dianion 12– as para‐cyanophenylating reagent for neutral benzonitriles is described. Neutral participants are varied to reveal the scope of applicable substrates and to evaluate the electronic and structural factors governing the regioselectivity and efficiency of the cross‐coupling. Benzonitriles substituted with Me, OMe and F provide the corresponding dicyanobiphenyls in good yields. The regularities in the reactivities are interpreted in terms of a reaction scheme involving the intermediacy of a charge‐transfer complex between 12– and benzonitrile, which transforms into a dimeric dianion either through a heterolytic pathway and/or by successive single electron transfer and recombination of the primary generated radical anions. Quantum chemical calculations of the structure and energy of the principal reaction intermediates match the experimental data. CV measurements of the new dicyanobiphenyls are also included.

Abstract2‐ and 3‐Substituted 4,4′‐dicyanobiphenyls are obtained by a concise and noncatalytic method using the in situ generated terephthalonitrile dianion as para‐cyanophenylation reagent.

Radical anions (RAs) are the key intermediates of the selective hydrodefluorination of polyfluoroarenes. We used the techniques of optically detected electron paramagnetic resonance (OD EPR), time-resolved fluorescence, time-resolved magnetic field effect (TR MFE), and the density functional theory to study the possibility of RAs formation from 4-aminononafluorobiphenyl (1) and pentafluoroaniline (2) and estimate their lifetimes and decay channels. To our knowledge, both RAs have not been detected earlier. We have registered the OD EPR spectrum for relatively stable in nonpolar solutions 1(-•) but failed to register the spectra for 2(-•). However, we have managed to fix the 2(-•) by the TR MFE method and obtained its hyperfine coupling constants. The lifetime of 2(-•) was found to be only a few nanoseconds. The activation energy of its decay was estimated to be 3.6 ± 0.3 kcal/mol. According to the calculation results, the short lifetime of 2(-•) is due to the RA fast fragmentation with the F(-) elimination from ortho-position to the amine group. The calculated energy barrier, 3.2 kcal/mol, is close to the experimental value. The fragmentation of 2(-•) in a nonpolar solvent is possible due to the stabilization of the incipient F(-) anion by the binding with the amine group proton.

Chemical stability of primary radical cations (RCs) generated in irradiated matter determines substantially the radiation resistance of organic materials. Transformations of the RCs of the glyme molecules, R(-O-CH2-CH2-)nO-R (R = CH3, n = 1-4) has been studied on the nanosecond time scale by measuring the magnetic field effects in the recombination fluorescence from irradiated liquid solutions of the glymes. In all cases, the RCs observed were different from that expected for the primary ones and revealed very similar hyperfine couplings independent of the poly(ethylene oxide) chain length and of the substitution of terminal methyl groups by C2H5 or CH2CH2Cl, as has been shown with diglyme as an example. Quantum chemical analysis of possible chemical transformations for the monoglyme RC as a model system allowed us to discover the reaction pathway yielding the methyl vinyl ether RC. The pathway involves intramolecular proton transfer followed by C-O bond cleavage. Only one (-O-CH2-CH2-O-) fragment is involved in this transformation, which is nearly barrierless due to the catalytic effect of adjacent glyme molecules. The rapid formation of the methyl vinyl ether RC in the irradiated monoglyme was confirmed by the numerical simulation of the experimental curves of the time-resolved magnetic field effect. These findings suggest that the R'-O-CH═CH2(•+) formation is a typical decay pathway for the primary RCs in irradiated liquid glymes.