Nitrobenzene Radical Anion Research Articles

Synthesis of nitrobenzene radical anion in a matrix and its IR absorption spectrum

1. The radical anion of nitrobenzene is prepared by reacting atomic sodium with nitrobenzene in a nitrobenzene matrix at 77°K. 2. For the first time, the complete IR spectrum of the crystalline nitrobenzene radical anion has been measured in the 400–3800 cm−1 range.

Association of radical anions alkali metal cations. III. Experimental and theoretical study of the associates of nitrobenzene radical anions with Li+, Na+, K+, Cs+ and (n-C4H9)4N+ cations

The nitrobenzene radical anion prepared by electrolysis was studied by UV spectroscopy. Formation of associates with Li+, Na+, K+, Cs+ and n(C4H9)4N+ cations was examined. It has been found that associates are also formed in a polar medium such as dimethylformamide. The enthalpy of the associated-free ion equilibrium was estimated as being equal to 6+4 kJ/mol-1. The quantum-chemical LHP method (in the π-approximation) was employed to study a simple ion pair model used for calculation of the most stable geometrical structure.

Electron spin resonance studies of ion association. Part 8.—Effects of ion-pairing on14N hyperfine splittings in p-substituted nitrobenzene anions

The nitro group 14N hyperfine splittings have been measured for the radical anions of nitro-benzene, p-nitrotoluene, p-nitroanisole, p-nitrobenzaldehyde and p-nitrobenzonitrile prepared by reduction with lithium, sodium, potassium or caesium in dimethoxyethane, tetrahydrofuran or methyltetrahydrofuran. The values observed form a pattern which can be rationalised quantitatively using a simple inductive model to describe the anion–cation interaction.

The mechanism of electroreduction of nitrobenzene and 3-nitropyridine in DMF in the presence of divalent cations

The differences in electrochemical behaviour of nitrobenzene and 3-nitropyridine connected with a change of supporting electrolyte are discussed. It is shown that in the presence of alkaline earch metal cations a deposit of composition (NB −. Me 2+ ) is formed at the electrode surface. The cations: Ba 2+ , Ca 2+ and Mg 2+ cause the instability of the nitrobenzene radical anion formed in the first electroreduction step. It was found that in the presence of Ba 2+ and Ca 2+ the NOB/NO −. couple is stabilized.

The mechanism of electroreduction of nitrobenzene and 3-nitropyridine in DMF in the presence of divalent cations

The differences in electrochemical behaviour of nitrobenzene and 3-nitropyridine connected with a change of supporting electrolyte are discussed. It is shown that in the presence of alkaline earch metal cations a deposit of composition (NB −. Me 2+) is formed at the electrode surface. The cations: Ba 2+, Ca 2+ and Mg 2+ cause the instability of the nitrobenzene radical anion formed in the first electroreduction step. It was found that in the presence of Ba 2+ and Ca 2+ the NOB/NO −. couple is stabilized.

Formation of Mn4+ centers in MgO powder due to nitrobenzene treatment in liquid phase

MgO powders activated in vacuo at 400°C and impregnated with nitrobenzene were investigated by ESR spectroscopy. The formation of Mn4+ centers due to electron transfer between nitrobenzene and impurity centers was established. Liquid impregnation yields substantially fewer nitrobenzene anion radicals than vapor-contact between the catalyst and nitrobenzene.

Reaction of electrogenerated nitrobenzene radical anion with alkyl halides

Reaction of electrogenerated nitrobenzene radical anion with alkyl halides

ChemInform Abstract: ESR INVESTIGATION OF THE NITROBENZENE ANION RADICAL IN SINGLE CRYSTALS OF BENZOATE SALTS

ESR spectra have been obtained and interpreted for the nitrobenzene anion radical in single crystals of two benzoate salts. In trimethylphenylammonium benzoate, [(CH3)3C6H5N]+[C6H5CO2]−, there is a single magnetically unique site per unit cell, so reasonably simple spectra result. Principal values for the g tensor and the hyperfine tensors of N and the ortho and para protons are reported. Splitting by the meta protons was not resolved. The single crystal ESR data for the nitrobenzene anion radical doped into benzoate sites in this hosts, together with the unit cell dimensions and symmtery obtained from single crystal x‐ray measurements on the host enabled a partial crystal structure determination. The crystals are monoclinic with four formula units per unit cell and are of C2/c symmetry with the four benzoate anions lying in special positions on a twofold axis such that the molecular twofold axis of each benzoate anion points along the b axis. Each of the four trimethylphenylammonium cations is likewise c...

ESR investigation of the nitrobenzene anion radical in single crystals of benzoate salts

ESR spectra have been obtained and interpreted for the nitrobenzene anion radical in single crystals of two benzoate salts. In trimethylphenylammonium benzoate, [(CH3)3C6H5N]+[C6H5CO2]−, there is a single magnetically unique site per unit cell, so reasonably simple spectra result. Principal values for the g tensor and the hyperfine tensors of N and the ortho and para protons are reported. Splitting by the meta protons was not resolved. The single crystal ESR data for the nitrobenzene anion radical doped into benzoate sites in this hosts, together with the unit cell dimensions and symmtery obtained from single crystal x-ray measurements on the host enabled a partial crystal structure determination. The crystals are monoclinic with four formula units per unit cell and are of C2/c symmetry with the four benzoate anions lying in special positions on a twofold axis such that the molecular twofold axis of each benzoate anion points along the b axis. Each of the four trimethylphenylammonium cations is likewise constrained under C2/c symmetry to possess either twofold or centrosymmetric symmetry, which necessitates an orientational disorder (not uncommon for tetraalkylammonium cations). In lithium benzoate–dimethylsulfloxide there are four magnetically inequivalent sites in the unit cell. The crystal structure of this host was determined in order to evaluate the principal values for the g tensor and the hyperfine tensors by spectral simulation. Eight formula units crystalize in a monoclinic unit cell P21/c. Two crystallographically distinct complexes were found. In one, the benzoate anion is essentially planar, whereas in the other complex, the CO2 group of the benzoate anion is twisted 8.2° with respect to the benzene ring. Although the chemical environment of the two crystallographically independent benzoate anions is similar, packing and Coulombic forces on the oxygen atom of one of the CO2 groups apparently twist this group out of the plane of the benzene ring. A most interesting feature of this structure is that, instead of the expected three-dimensional array of ions, there exist polymer chains of composition [Li+(C6H5CO2)−⋅ (CH3)2SO]∞ which are propagated by inversion symmetry in the direction of the b axis. The spacing between polymer chains is that characteristic of van der Waals forces, hence the packing of this benzoate salt behaves essentially as an ionic crystal in one dimension, but as a molecular crystal in the other two dimensions. Principal values and axes of the g tensor and the hyperfine tensors are also reported for the nitrobenzene anion radical in this host. In both hosts the para proton hyperfine tensor was found to be that expected for an isolated R2C–H fragment, whereas the ortho proton hyperfine tensor is twisted about 20° with respect to the C–H bond. The data are consistent with a preferred planar geometry for the nitrobenzene anion. A new method for incorporating electrochemically generated ion radicals, which are difficult to isolate, into single crystals of diamagnetic host suitable for ESR studies is also reported.

Solvation of the nitrobenzene radical anion

An electrostatic solvation model within the INDO approximation, representing the interaction with the solvent by means of an effective solvent field, is applied to the nitrobenzene radical anion. The available solvent sensitivity data for the 1H, 13C, 14N and 17O hyperfine coupling constants are satisfactorily reproduced. The results are consistent with the assumption of a planar structure of the radical, in contrast with the results of a recent theoretical study.

ESR Studies of Nitrobenzene Ion-Pair Equilibria in N,N-Dimethylformamide

Abstract The hyperfine splitting constants of the nitrobenzene radical anion in DMF vary with the type of the counter cations and the concentrations. The tendency of these variations is related to the shift of the half-wave reduction potential of nitrobenzene. The variation of the nitrogen 14N hyperfine splitting constant is attributable to the formation of ion pairs involving the nitrobenzene radical anion and its counter cation. The ion-pair formation constants were evaluated from the changes in the hyperfine splitting and are completely consistent with those obtained from polarographic studies.

Quantum-chemical approach to the ion pair formation (IPF) equilibrium constants of nitrobenzene radical anions with univalent cations and water molecul

The simple HMO method extended to problems of ionic association of cations with organic radical anions by McClelland [1] and Goldberg and Bolton [2] was successfully used not only in the case of ion pair formation between nitrobenzene radical anion and univalent cations (eqn. (1)) but also when interactions are between this radical and water molecule (eqn. (2)). p]Inspection of a plot of log K ass against E HMO ass for eqns. (1) and (2) leads to the conclusion that the treatment considered here, although very empirical, can be applied advantageously to prediction of association constants for equilibria like (1) and (2). The simplicity of this treatment suggests wide applications for more complex systems.

Electron spin resonance investigation of carbon-13 hyperfine interactions in nitrobenzene anion radical

Synthesis of carbon-13 enriched nitrobenzene which contains 22·5 mole per cent of nitrobenzene-1-13C and an equal amount of nitrobenzene-4-13C has been accomplished. We report the carbon-13 hyperfine interactions in the corresponding anion radicals in a variety of solvent media. In hexamethylphosphoramide a C1 = -7·05 gauss and a C4 = 6·14 gauss. These couplings change to -9·03 gauss and 5·31 gauss, respectively, when the solvent medium is dimethylformamide containing 0·598 mole fraction of water. The solvent dependence of a C1 is consistent with the radical remaining planar as opposed to adopting a pyramidal conformation at the nitrogen when hydrogen bonds form between the radical anion and protic solvents. Data reported here provide an experimental means to estimate the spin density distribution in nitrobenzene anion.

The nature of active sites on TiO 2 and TiO 2SiO 2 for the isomerization of butenes

The isomerization of 1-butene and cis-2-butene was studied over TiO 2 and TiO 2SiO 2 having different mole ratios with various treatments on the surface. The activity decreased with increasing the evacuation temperature on both catalysts. The ratio of cis/trans-2-butene from 1-butene increased when TiO 2 and TiO 2SiO 2 were evacuated above 400 and 500 °C, respectively. Oxygen treatment of the catalysts evacuated at 450 °C decreased the activity of TiO 2 but increased that of TiO 2SiO 2. Hydrogen treatment showed the opposite effect to that of oxygen. Ti 3+ were produced on the surface by the evacuation above 300 and 400 °C on TiO 2 and TiO 2SiO 2, respectively. On these surfaces the nitrobenzene anion radicals were formed by electron transfer to nitrobenzene from Ti 3+ and Ti 2+. The change in nature of active sites after several treatments was discussed in terms of surface acidity and electron donating property.

Equilibrium studies by electron spin resonance. IX. Free energies of hydrogen bonding to substituted nitrobenzene anion radicals

Equilibrium studies by electron spin resonance. IX. Free energies of hydrogen bonding to substituted nitrobenzene anion radicals

Copolymers of acrylonitrile and α‐methyleneglutaronitrile as model compounds for polyacrylonitrile initiated by the nitrobenzene radical anion in tetrahydrothiophene 1,1‐dioxide

AbstractThe copolymerization constants for the radically initiated system acrylonitrile (AN)/α‐methyleneglutaronitrile (MGN) in bulk were determined by means of IR spectra using a base‐line technique and independently by means of NMR spectra. The constants obtained from the IR spectra were whereas those from the NMR measurements were The IR spectrum of polyacrylonitrile, obtained by anionic polymerization and initiation with the electrochemically generated nitrobenzene radical anion in sulfolane (tetrahydrothiophene 1,1‐dioxide), has been established to correspond to an AN‐MGN copolymer structure having on an average 4 to 6 ß‐cyanoethyl units per 10 backbone acrylonitrile units. A competitive addition‐prototropy mechanism is suggested to explain the formation of cyanoethyl groups.

Solvation of nitroaromatic radical anions : a molecular orbital investigation of hydrogen bonding models

SCF calculations employing the INDO approximation have been applied to a study of the interaction of water and the nitrobenzene radical anion in order to examine possible mechanisms by which electron spin resonance hyperfine coupling constants are altered when the solvent medium containing the radicals is changed from aprotic to hydroxylic. Calculations have been carried out for hydrogen-bonded radical-water complexes of nine different geometries. None of these calculations agree adequately with the available experimental data. Much better agreement with experiment is obtained if the hydrogen-bond formation is accompanied by a distortion of the nitro group toward a pyramidal conformation. The calculations indicate that this pyramidal distortion, rather than a rotation of the nitro group with respect to the aromatic plane, accompanies hydrogen-bond formation and suggests an experimental method of testing the prediction.

Polarographic investigation of the interactions between nitrobenzene radical anions, water and univalent cations in dimethylformamide/water mixtures

Dependences of the half-wave potential of the first reduction wave of nitrobenzene in 0.1 M Li + , Na + , K + and Et 4 N + perchlorates in DMF on varied amounts of water were studied polarographically. At fixed concentrations of water ( cf. Table 1) plots of E 1/2 against the logarithm of the Na + concentration have been made and respective composition of associate species were determined. Extension of the Peover-Davies method of evaluating the equilibrium constants of ion-pair formation from polarographic measurements has been given. From the analysis of polarographic data equilibrium constants have been determined for associates like (NB ⨪ , H 2 O), and partial equilibrium constants for the system (NB ⨪ , Na + )/(NB ⨪ , 2Na + ). The dependence of activity coefficients of H 2 O in DMF on the composition of the mixture is given.

Polarographic investigation of the interactions between nitrobenzene radical anions, water and univalent cations in dimethylformamide/water mixtures

Summary Dependences of the half-wave potential of the first reduction wave of nitrobenzene in 0.1 M Li + , Na + , K + and Et 4 N + perchlorates in DMF on varied amounts of water were studied polarographically. At fixed concentrations of water ( cf. Table 1) plots of E 1/2 against the logarithm of the Na + concentration have been made and respective composition of associate species were determined. Extension of the Peover-Davies method of evaluating the equilibrium constants of ion-pair formation from polarographic measurements has been given. From the analysis of polarographic data equilibrium constants have been determined for associates like (NB ⨪ , H 2 O), and partial equilibrium constants for the system (NB ⨪ , Na + )/(NB ⨪ , 2Na + ). The dependence of activity coefficients of H 2 O in DMF on the composition of the mixture is given.

Electron donor sites on the surface of magnesium oxide powder studied by electron spin resonance spectroscopy

The electron donor properties of MgO powders, activated in vacuo in the temperature range 300–1200 K have been investigated by adsorption of nitrobenzene and some of its para substituted derivatives.The results confirm that the donor properties of MgO are an intrinsic property of the surface, being practically independent of impurity. Two types of nitrobenzene radical were detected: the first one, formed on low temperature activated samples (<1200 K), is the nitrobenzene radical anion interacting with surface protons; the second one, observed on high temperature (1200 K) activated MgO, is the “free” radical anion.No correlation between electron affinity of the adsorbed molecules and radical surface concentration was found. The proton affinity of the anion radical has to be taken into account to rationalize the results. A model of the electron donor surface site consisting of a dual site (O2–cus, OH–) is presented.The effect of adding Ni2+ ions in solid solution has also been examined.