Out-of-Plane Distortions of Chlorinated Nitrobenzene Radical Anions

According to UHF/INDO calculations of the model conformations of the chlorinated nitrobenzene radical anions, the rotation of the nitro group relative to the plane of the benzene ring is accompanied by its pyramidal deformation caused by the pseudo-Jahn–Teller effect. The degree of the structural distortions of the chlorinated nitrobenzene radical anions depends on the arrangement of the chlorine atoms in the benzene ring and on the solvent, increasing from DMF to its mixtures with water. The isotropic hyperfine coupling constants and their dependence on the water content in a binary mixture of solvents are interpreted for a number of chlorinated nitrobenzene radical anions.     

Indo study of the angular dependences of isotropic hyperfese interaction constants in the model conformations of the nitrobenzene radical anion

The UHF/INDO calculations of the model conformations of the nitrobenzene radical onion show that rotation of the nitro group relative to the plane of the benzene ring is accompanied by a pyramidal distortion of the group caused by the pseudo-Jahn-Teller effect (vibronic interaction between the ground n and totally symmetric lowest excited σ states). The angular dependences of the¹⁴N,¹³C,¹H, and¹⁷O Isotropic hyperfine interaction constants are analyzed. Experimental ESR data are interpreted for the radical anions of nitrobenzene derivatives with ortho-alkyl groups. Translated fromZhumal Strukturnoi Khimii, Vol. 41, No. 3, pp. 457-467, May-June, 2000.     

Solvation Dependences of Isotropic Hyperfine Interaction Constants and out-of-Plane Distortions of ortho-Substituted Nitrobenzene Radical Anions

For a number of ortho-substituted nitrobenzene radical anions (RAs) generated in DMF and its binary mixtures with water, it is shown that for radical anions with a substituent of minor effective volume in one ortho position to the nitro group, the dependences of the isotropic hyperfine interaction (ihfi) constants on the mole fraction of water are S-like and dictated by the medium composition and the concerted out-of-plane rotational and pyramidal distortions of the nitro group of the radical anion. The S-like shape of the solvation dependences of the ihfi constants is dictated by the dominant rotational distortions of the nitro group. For most radical anions with two ortho substituents or with one ortho substituent with a large effective volume, the S-like dependences are not observed, and the values of the nitrogen ihfi constants depend on the dominant pyramidal distortion of the nitro group. For the 2-tert-butylnitrobenzene radical anion in water, the nitrogen ihfi constant is a_N=25.62 G, which is typical of nitroaliphatic radical anions. This effect is explained based on the pyramidal structure of the nitro group in the case of its large rotation angles.     

Solvation thermodynamics of benzene,nitrobenzene, and aniline in water–acetonitrile mixtures

The enthalpies of dissolution of benzene, nitrobenzene, and aniline in water–acetonitrile mixtures are determined via calorimetry. The concentration dependences of the standard enthalpies of solvation of solutes are calculated. It is found that the concentration dependences of the standard enthalpies of solvation pass through maxima. The height of the observed maxima is shown to depend largely on the nature of the substituent. In the presence of a hydrophilic amino group capable of forming strong hydrogen bonds with water molecules, the value of a maximum falls; in the presence of a nitro group, it rises. The enthalpy parameters of pair interaction between molecules of water and benzene and its derivatives are calculated.     

Effect of the structure of the aromatic system on the rate of dimerization of radical anions of aromatic nitro compounds

The radical anions formed in the first stage of electrolytic reduction of 9-nitroanthracene, 1-nitronaphthalene, and nitrobenzene enter into a secondorder reaction in which the value of the rate constant increases as the degree of localization of the unpaired electron on the reaction site increases.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1492–1495, July, 1990.     

Volumetric behaviour of binary liquid mixtures of dimethylsulphoxide with substituted benzenes at 303.15 k

Excess molar volumes (V ^E ) for binary mixtures of dimethyl sulphoxide (DMSO) with substituted benzenes have been measured at 303.15?K. The substituted benzenes include toluene, ethylbenzene, chlorobenzene, bromobenzene and nitrobenzene. The measured V ^E data is positive for the mixtures of DMSO with nitrobenzene and is completely negative over the entire composition range in the mixtures of toluene, ethylbenzene and chlorobenzene and an inversion in sign is observed in the bromobenzene system. The experimental results are analysed in terms of intermolecular interactions and effect of substitutents on benzene ring between unlike molecules.     

聚苯基（聚苄基）甲基硅氧烷的氟烷基化反应研究

通过苯基甲基二乙氧基硅烷和苄基甲基二乙氧基硅烷的缩合反应制备了聚苯基甲基和聚苄基甲基硅氧烷。研究了它们与含氟酰基过氧化物间的反应。经酸碱滴定及ＩＲ、＾１Ｈ ＮＭＲ和＾１９Ｆ ＮＭＲ光谱分析确证反应主要生成苯环上氟烷基取代产物。通过测定经氟烷基化后聚硅氧烷处理的玻璃表面的接触角，初步评价了氟烷基化率对其表现性能变化的影响。     

Reductive Activation of Arenes: XIV. Effect of Medium on the Products Ratio in the Alkylation of Nitrobenzene Radical Anion Sodium Salt

The product of nitrobenzene reduction by 1 equiv of sodium reacted with tert-butyl iodide in liquid ammonia and its mixtures with tetrahydrofuran and hexamethylphosphoramide to afford a mixture of compounds alkylated either by the functional group (N-alkylation) or at the benzene ring (C-alkylation). The ratio of N- and C-alkylation products decreases in the solvents series NH₃-THF (5.7) > NH₃ (1.0) > NH₃-HMPA (0.6).     

Heats of Mixing of Aqueous Solutions of Alkali Metal Salts of Substituted Benzenesulfonic Acids

The enthalpy change on mixing aqueous solutions of substituted benzene sulfonic acids and their salts, with salts having a common cation or anion, were measured at constant total ionic strength and at 25°C. The results are qualitatively interpreted in terms of solute–water structural properties and the ion size effect. The heat effects of mixing solutions having common anions obey the sign rule of Young and Smith. In anion–common cation mixings at concentration of 0.5 mol-kg^–1 only exothermic heat effects were observed, whose magnitude increase with the increasing difference in size of the mixed anions. The magnitude of the mixing effect increased with the salt concentration in cation–common anion mixing processes, In anion–common cation mixings the enthalpy of mixing changes sign from negative to positive, indicating a predominantly endothermic effect as concentration increases.     

Laser-induced pinpoint hydrogen evolution from benzene and water using metal free single-walled carbon nanotubes with high quantum yields

Metal-free photocatalytic hydrogen evolution occurred efficiently in benzene containing single-walled carbon nanotubes under laser irradiation at 532 nm with an extremely high turnover number of 2 000 000 and a high quantum yield of 130%. The rate of hydrogen evolution increased with increasing laser intensity to exhibit a fourth power dependence, suggesting that hydrogen was evolved via four-photon processes in which the coupling of two radical anions derived from benzene is the rate-determining step and the benzene radical anion is produced by electron transfer from benzene to the doubly excited state of single-walled carbon nanotubes, which requires two photons. Polymerisation of benzene was induced by the photogenerated C₆H₆˙^–, accompanied by hydrogen evolution, resulting in a leverage effect to increase the quantum yield of hydrogen evolution to well over the 25% expected for the four-photon process. Laser-induced hydrogen evolution also occurred in water containing single-walled carbon nanotubes. In contrast to the case of benzene, water was not oxidized but hydrogen evolution from water was accompanied by the multi-oxidation of single-walled carbon nanotubes. The yield of hydrogen based on one mole of single-walled carbon nanotubes with 1.4 nm diameter and 1–5 mm length was determined to be 2 700 000%, when oxidations of single-walled carbon nanotubes occurred to produce the polyhydroxylated product.     

Free radicals of electrochemical reduction of derivatives of 3-nitro-1,4-dihydropyridines

By means of ESR, under conditions of eletrochemical generation of particles, the formation of four types of secondary free radicals has been confirmed in the process of electrochemical reduction of molecules of N-unsubstituted derivatives of 3-nitro-1,4-dihydropyridine in dimthylformamide — specifically, a dianion radical of the molecule of the original compound; an anion radical of the corresponding isomeric 4,5-dihydropyridine; a radical of the nitroalkane type; and in addition, for the compound substituted with a nitrobenzene group; a free radical with the nitrobenzene structure. Methods for synthesis of the individual compounds are described, and a scheme is presented for the mechanism of their electrochemical conversion.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 355–364, March, 1995. Original article submitted February 21, 1995.     

Polarographic study of the conduction of the polar effect of a substituent through the furan ring and side bridge groupings

The coefficients of conduction of the polar effect of a substituent through the furan ring and side bridge groupings were calculated by comparison of the polarographic half-wave potentials for the electroreduction of the nitro group in series of 5-substituted derivatives of 2-nitrofuran and p-substituted nitrobenzene derivatives by means of the - method. The polarographic method can be successfully used for this purpose in media in which the electrochemical process is not limited by the kinetics of the side process of surface protonation of the nitro group. It follows from the polarographic data and hyperfine structure of the ESR spectra of the anion radicals that the furan ring conducts the polar effect of substituents better (by a factor of 1.1–1.2) than the benzene ring. Depending on the electronic structure of the bridge groups, the introduction of bridge groups between the furan ring and the substituent decreases the conduction of the effect of substituents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1309–1312, October, 1972.     

Regioselective functionalisation of nitrobenzene and benzonitrile derivatives via nucleophilic aromatic substitution of hydrogen by phosphorus-stabilized carbanions

The synthesis of P-benzylic products by reaction of anions stabilised by N-phosphorylphosphazenyl, N-methoxycarbonylphosphazenyl, phosphine borane complex, and phosphine oxide groups by displacement of hydrogen of a variety of electron-deficient benzene derivatives is described. Lithium phosphazenes were the most suitable nucleophiles for the substitution of hydrogen in nitrobenzene and some ortho-, meta-, and para- substituted nitrobenzenes. Lithiated phosphine borane complexes produced efficiently the substitution of the hydrogen at the para position of a cyano group in cyanobenzenes, whereas the anion of ethyldiphenylphosphine oxide lead to complex mixtures with all electrophiles assayed. The method reported here represents a convenient alternative to the vicarious nucleophilic substitution for the synthesis of benzylic phosphorus derivatives using phosphorus-stabilised anions that do not bear a leaving group at the carbanionic centre.     

Thermodynamic Characteristics of Resolvation of Bromide Ions in Water–Dimethyl Sulfoxide Mixtures

Real and chemical thermodynamic characteristics of resolvation of bromide ions in water–dimethyl sulfoxide mixtures and a surface potential of dimethyl sulfoxide are presented and analyzed. The data are obtained by the method of Volta potential differences. The real thermodynamic characteristics of the bromide ion transport are positive (as those of the chloride ion studied earlier). This is due to structural rearrangement of the surface layer at the solution/gas interface when passing from water to water–organic substance mixtures. According to an analysis of the chemical energy of the bromide ion resolvation, anions that are capable of forming hydrogen bonds with proton-donor solvents are weakly solvated in aprotic solvents.     

Thermodynamics of Resolvation of Sodium and Potassium Ions in Water–Dimethylformamide

The real primary medium effect of sodium and potassium ions and the real Gibbs energy of transfer of these ions from water into a mixed water–dimethylformamide (DMF) solvent are determined using the method of Volta potential differences at 298.15 K. For DMF, the surface potential at the solvent/gas interface is found to equal –0.434 V. Based on this value, chemical thermodynamic characteristics of the ions are calculated. The thermodynamic characteristics for resolvation of cations are compared with those for anions in the mixtures under investigation obtained earlier.     

ESR. Spectra of the Radical Anions of Cycloalkylbenzenes

Radical anions of five cycloalkylbenzenes (alkyl = propyl, butyl, pentyl, hexyl, or heptyl) have been studied by ESR. spectroscopy at ?90°C. In the case of cyclopropylbenzene, no reliable experimental data could be obtained, because of the instability of its radical anion. The spectra of the radical anions of the four higher homologues have been analysed by means of a computer program. The assignment of the coupling constants to the α-protons in the para position of the benzene ring and to the cycloalkyl ß-protons has been based on the spectra of specifically deuterated derivatives. The experimental data of the radical anion of cycloalkylbenzenes have been compared with those of the radical anions of five alkylbenzenes (alkyl = methyl, ethyl, n-propyl, isopropyl, or t-butyl), the spectra of the latter being reexamined at ?90°C. In the cycloalkyl series the degeneracy of the two benzene-type lowest antibonding orbitals is the more effectively removed the larger the substituent, whereas the reverse relation holds for the non-cyclic series. The preferred conformation of the substituents is that in which the alkyl or cycloalkyl ß-proton is near to the nodal plane of the benzene π-system, and this preference is accentuated with the increasing size of the substituent group.     

A comparative effect of ring annelation on cation-benzene and anion-benzene

DFT/B3LYP calculations were carried out on several π-complexes formed by cations and anions with annelated benzene, respectively. The binding energies obtained with standard method were corrected by basis set superposition error (BSSE) and zero-point energy (ZPE) during the geometry optimization for all complexes at the same levels of theory, respectively. Some different aspects of the π–cation have been compared to those of π–anion, involving in binding energy changes in effect of ring annelation, the aromaticity of the ring upon complexation, Mulliken and NBO charge-transfer. The effect of BSSE correction during the optimization is very important in some π–anion complexes whether or not using diffuse functions in basis set, and results with at least one set of diffuse functions 6-31+G(d) basis set is a little better than results obtained by 6-31G(d, p) basis set for some π–anion especially for F⁻ complexes.     

Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives

The electron delocalization of benzene (C₆H₆) and hexafluorobenzene (C₆F₆) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R²>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C₆ skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C₆H_(6−n)F_n, where n=1–5).     

Ionic association in hydrogen-bonding solvents

Studies on ionic association in hydrogen-bonding solvents including water, aliphatic alcohols, fluorinated alcohols, formamide, ethylene glycol, and propanol-acetone mixtures are compared. Data were derived from measurements of conductivity, ultrasonic absorption, and viscosity of electrolyte solutions and diffusion of nonelectrolytes. It is concluded that electrolyte solvents can be divided into three categories according to whether they solvate effectively cations only, anions only, or both cations and anions. Water and most other hydrogenbonding solvents constitute the third class, a group in which patterns of ionic aggregation are very similar. Fluorinated alcohols belong to the second class, showing significantly different ion-pairing behavior.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.