Electronic structure of 1,3-dinitrobenzene radical anion: A multiconfigurational quantum chemical study

The structure of 1,3-dinitrobenzene radical anion in the doublet ground and lowest excited states was studied by ab initio multiconfiguration CASSCF methods. The results of calculations suggest the existence of one symmetrical and two asymmetrical structures of the radical anion. The energies of these structures were estimated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2645–2647, December, 2005.     

超氧负离基研究: 无水乙腈中超氧负离子基的稳定性及其捕获

考察了影响无水乙腈中超氧负离子基(O2^-)稳定性的因素,发现氧促使乙腈中O2^-浓度迅速减小,通过产物鉴定和UV动力学分析提出氧促O2^-与乙腈反应的可能机理。研究了O2^-与2,2,6,6-四甲基-4-羟基-N-溴哌啶(NB)的反应,表明NB可望成为非水溶剂中O2^-的专一捕获剂。     

Interpreting the solvent dependence for the rate of electron exchange between tetracyanoquinodimethane and its anion radical

An approach previously devised is used in interpreting the observed solvent dependence of the rate of electron exchange between tetracyanoquinodimethane and its anion radical, as it incorporates effects from strong interaction in electrontransfer reactions involving intramolecular rearrangement. The kinetic characteristics have been derived, for which satisfactory values have not been obtained in the interpretation based on the traditional approach.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 353–357, May–June, 1987.I am indebted to L. D. Zusman for directing attention to [4].     

"Abnormal" salt and solvent effects on anion/cation electron-transfer reactions: an interpretation based on Marcus-Hush treatment

Salt and solvent effects on the kinetics of the reactions [Fe(CN)6]3- + [Ru(NH3)5pz](2+) right arrow over left arrow [Fe(CN)6]4- + [Ru(NH3)5pz]3+ (pz = pyrazine) have been studied through T-jump measurements. The forward and reverse reactions show different behaviors: "abnormal" salt and solvent effects in the first case and normal effects in the second one. These facts imply an asymmetric behavior of anion/cation reactions depending on the charge of the oxidant. The results can be rationalized by using the Marcus-Hush treatment for electron-transfer reactions.     

HSCCS自由基势能面的理论研究

在CCSD(T)/6-311G(d,f)//MP2/6-311G(d,f) ZPE水平下,计算得到含有8个异构体和11个过渡态的HSCCS自由基体系势能面,讨论了异构体的结构与稳定性及异构体之间的异构化过程.结果表明异构体m1的能量最低,除m1以外,异构体m2和m3的能量也比较低,在MP2水平上,过渡态TS1的能量比异构体m2仅高3.9kJ/mol,而在CCSD(T)水平上,TS1的能量比m2低14.6 kJ/mol,这说明异构体m2可以迅速转化为能量更低的m1.异构体m3的能量比异构体m1高49.99 kJ/mol,可以推断,在合适的实验条件下可以观测到异构体m1.     

Time-dependent density functional theory study on intramolecular charge transfer and solvent effect of dimethylaminobenzophenone

The lower singlet excited states for dimethylaminobenzophenone have been investigated as a function of the twisting motion with inclusion of solvent effects. Theoretical calculations have been performed using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with a 6-311+G(2d,p) basis set have been used to compute transition energies. The solvent effects have been described within the polarizable continuum model. Ground-state geometries are optimized using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d) basis sets. Vertical absorption energy calculations characterize the lower singlet excited states both in vacuum and in different kinds of solvents. A large redshift of the absorption maximum in the polar solvent suggests an intramolecular charge transfer character of the excited state. We have constructed the potential energy curves of two possible twisting motions of the excited states both in vacuum and in the polar solvent of acetonitrile: the twisting of only the dimethylamino group and the twisting of the dimethylaminophenyl group with respect to the benzoyl group. Both twisting processes predict the formation of the twisted intramolecular charge transfer state associated with the crossing of a low barrier. The presence of the polar solvent significantly changes the shape of the energy curves. Calculated emission energies for both the isolated and the solvated systems show a large Stokes shift between the absorption and fluorescence maxima. Two possible twisting motions produce similar fluorescence spectroscopic consequences. Our results including solvent effects explain the weak "dual-fluorescence" feature of dimethylaminobenzophenone, and imply that the two possible twisting motions may occur in the excited-state relaxation dynamics, but the twisting of the dimethylamino group seems to take place easier.     

Theoretical study of the electronic excited states of tetracyanoethylene and its radical anion.

The low-lying electronic states of tetracyanoethylene (TCNE) and its radical anion were studied using multiconfigurational second-order perturbation theory (CASPT2) and extended atomic natural orbital (ANO) basis sets. The results obtained yield a full interpretation of the electronic absorption spectra, explain the spectral changes undergone upon reduction, give support to the occurrence of a bound excited state for the anionic species, and provide valuable information for the rationalization of the experimental data obtained with electron transmission spectroscopy.     

Time-dependent density functional theory study on hydrogen-bonded intramolecular charge-transfer excited state of 4-dimethylamino-benzonitrile in methanol

The time-dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen-bonded intramolecular charge-transfer (ICT) excited state of 4-dimethylaminobenzonitrile (DMABN) in methanol (MeOH) solvent. We demonstrated that the intermolecular hydrogen bond C[triple bond]N...H-O formed between DMABN and MeOH can induce the C[triple bond]N stretching mode shift to the blue in both the ground state and the twisted intramolecular charge-transfer (TICT) state of DMABN. Therefore, the two components at 2091 and 2109 cm(-1) observed in the time-resolved infrared (TRIR) absorption spectra of DMABN in MeOH solvent were reassigned in this work. The hydrogen-bonded TICT state should correspond to the blue-side component at 2109 cm(-1), whereas not the red-side component at 2091 cm(-1) designated in the previous study. It was also demonstrated that the intermolecular hydrogen bond C[triple bond]N...H-O is significantly strengthened in the TICT state. The intermolecular hydrogen bond strengthening in the TICT state can facilitate the deactivation of the excited state via internal conversion (IC), and thus account for the fluorescence quenching of DMABN in protic solvents. Furthermore, the dynamic equilibrium of these electronically excited states is explained by the hydrogen bond strengthening in the TICT state.     

Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile

We present results of the theoretical study and numerical calculation of the dynamics of molecular liquids based on the combination of the memory equation formalism and the reference interaction site model (RISM). Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density (pressure) dependence of translational diffusion coefficients D and orientational relaxation times tau for acetonitrile in water, methanol in water, and methanol in acetonitrile--all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the extended simple point charge model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and tau observed in real and computer experiments. In particular, anomalous behavior, i.e, the increase in mobility with density, is observed for D and tau of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.     

Dipole–reaction field interaction model for the solvent reorganization energy and its application to the benzoquinone–benzoquinone anion radical system

 Based on the spherical cavity approximation and the Onsager model, a dipole–reaction field interaction model has been proposed to elucidate the solvent reorganization energy of electron transfer (ET). This treatment only needs the cavity radius and the solute dipole moment in the evaluation of the solvent reorganization energy, and fits spherelike systems well. As an application, the ET reaction between p-benzoquinone and its anion radical has been investigated. The inner reorganization energy has been calculated at the level of MP2/6–31+G, and the solvent reorganization energies of different conformations have been evaluated by using the self-consistent reaction field approach at the HF/6–31+G level. Discussions have been made on the cavity radii and the values are found to be reasonable when compared with the experimental ones of some analogous intramolecular ET reactions. The ET matrix element has been determined on the basis of the two-state model. The fact that the value of the ET matrix element is about 10 times larger than RT indicates that this ET reaction can be treated as an adiabatic one. By invoking the classical Marcus ET model, a value of 4.9 × 10⁷M⁻¹s⁻¹ was obtained for the second-order rate constant, and it agrees quite well with the experimental one. Received: 19 October 2001 / Accepted: 17 January 2002 / Published online: 3 May 2002     

Mössbauer spectroscopic study of the temperature dependence of the intramolecular mobility of a cross-linked polymeric cation-exchanger based on acrylic acid

Conclusions The temperature transition of a solvated cross-linked polymer (the SGK-7 carboxyl cation-exchanger, which contains iron(III) ions) from the solid state to a state characterized by intense intramolecular motions was detected and studied by Mössbauer spectroscopy. Triggering of two types of motions was demonstrated: high-frequency vibrations of atoms with a higher amplitude (manifested by a sharp decrease in the probability of the Mössbauer effect) and slower (conformational) motions (manifested by a change in the shape of the spectrum). The parameters of the motions were determined within the framework of the lattice model and the effect of the solvating liquid on the nature of the transition was demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1740–1745, August, 1985.     

Theoretical calculation of vibrational polarizabilities. An application to the study of conformational and solvent effects

The vibrational polarizability tensor is linked to the force constant and dipole moment derivative matrices. The analytical computation of these quantities is possible, in particular by using semi-empirical quantum-chemical methods. The electrostatic influence of liquid surroundings can be analyzed with the help of a cavity model. Applied to a series of molecules, this method of calculation emphasizes the role of non-diagonal elements of the force constant matrix and the variation of the mean vibrational polarizability under the influence of a solvent, especially in the case of non-rigid molecules and hydrogen-bonded complexes.     

Comparative study of anionic and radical cyclization for the preparation of 1,3-dimethylindans: highly stereoselective preparation of cis-1,3-disubstituted indans via intramolecular carbolithiation

[reaction: see text] The preparation of 1,3-dimethylindans from 4-(2-bromophenyl)-1-pentene (1) and 2-(2-iodo-1-methylethyl)styrene (2) substrates via radical-mediated cyclization and intramolecular carbolithiation has been investigated. Although cyclization of the radical derived from either substrate proceeds with modest selectivity for the cis-isomer, as does cycloisomerization of the aryllithium derived from substrate 1 (cis/trans approximately 2), intramolecular cyclization of the alkyllithium derived from substrate 2 is a highly cis-selective process (cis/trans = 12).     

Theoretical study on influence of ligand and solvent to CdS clusters

Based on the experimental zinc blende and wurtzite structures of CdS nanocrystals, five new CdS clusters (Cd₃S₃, (Cd₃S₃)₂, (Cd₃S₃)₃, Cd₄S₄ with C_2V, and Cd₄S₄ with T_D symmetry) are investigated via optimization of their original structures at B3LYP/Lanl2dz theoretical level. Through considering integration influence of solvent and ligand, our calculated Raman and absorption spectra can be consistent with the reported experimental results. First, our calculated Raman peaks of Cd₃S₃, Cd₄S₄ (T_D), (Cd₃S₃)₂, and (Cd₃S₃)₃ are within the range of 260–290 cm^?1, which is also reported by experiment. Subsequently, for deep researching five clusters, the absorption spectra of them are calculated using time‐dependent DFT method. The wavelengths of the absorption peaks, which is calculated in solvent, increase in the order Cd₃S₃, Cd₄S₄ (T_D), (Cd₃S₃)₂, and (Cd₃S₃)₃. Moreover, the wavelengths of absorption peaks shift to blue in solvent, compared with those without solvent. Furthermore, our clusters are smaller than the size of the smallest CdS nanocrystals, the calculated absorption spectra of five clusters in solvent show obvious blue shift than the wavelengths of absorption spectra of reported CdS nanocrystals. This is induced by the quantum size effect. Besides, we further investigated the influence of ligands to CdS unit in aqueous condition. Through structures and characters analysis of S? Cd? SR, we discovered that ligands took important role during the formation of CdS nanocrystals in aqueous synthesis. Calculated results of spectra, bond length, and Wiberg bond index (WBI) values show that different ligands have similar influence on CdS unit. Moreover, using WBI values, we also confirm that Cd atom has stronger interaction with S in nanocrystals than that with S atom in ligand. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Thermochemistry of the fluoroformyloxyl radical: a computational study based on coupled cluster theory

The standard enthalpy of formation of FCO(2) (X (2)B(2)) was determined by a computational approach based on coupled cluster theory [CCSD(T)] with energies extrapolated to the basis-set limit, with additional corrections accounting for core-valence correlation, scalar relativity, spin-orbit coupling, and zero-point vibrational motions. Utilizing a variety of independent reaction schemes, our best estimate is Delta(f)H(o)(0)(FCO(2)) = -86.0 +/- 0.6 kcal mol(-1) [Delta(f)H(o)(298) )(FCO(2)) = -86.7 +/- 0.6 kcal mol(-1)], which is shown to be more accurate than previous theoretical and experimental values. The chosen computational procedure was also applied to HCO (X (2)A'), where we find excellent agreement with experiment, and to FCO (X (2)A'), where we recommend an improved value of Delta(f)H(o)(0)(FCO) = -42.1 +/- 0.5 kcal mol(-1) [ Delta(f)H(o)(298)(FCO) = -42.0 +/- 0.5 kcal mol(-1)]. Further theoretical results concern the C-F bond dissociation energy, electron affinity, ionization energy, first and second excitation energies in FCO(2), fluoride ion affinity of CO(2), and equilibrium geometries of the molecules treated presently. For FCO (X (2)A') we propose an improved equilibrium structure: r(e)(CF) = 132.5(2) pm, r(e)(CO) = 116.7(2) pm, and theta(e)(FCO) = 127.8(2)(o).     

Tail molecule dependence of thiolate adsorption on Au(111) surface: Theoretical study

The adsorption of thiolates with various tail molecules on the Au(111) surface has been investigated by first-principles calculations. We have considered six typical thiolate molecules, that is, methylthiolate, ethylthiolate, ethylenethiolate, acetylenethiolate, benzenethiolate, and thiophenethiolate. It is found that these thiolates exhibit little difference in their stable adsorption geometries. They are adsorbed at the bridge site with being significantly tilted from the surface normal. The adsorption energy of thiolate on Au, on the other hand, largely varies depending on the type of tail molecule, and is linearly proportional to the binding energy of thiolate with H. We discuss the tail molecule dependence in terms of the bonding environment around the C atom connected to the head S atom.     

Theoretical study of the changes in the electronic structure of benzonitrile accompanying its conversion into a radical anion

The electronic structure of benzonitrile and its radical anion have been investigated at different levels of ab initio MO theory: STO-3G, 6-31G and 6-31G^**. The changes in the electronic structure of the neutral molecule accompanying its conversion into the corresponding radical anion have been estimated. It was established that the radicalization leads to significant changes in the bond lengths with double and triple bond character expressed in the conjugated system. The distribution of the total atomic charges on transition from the neutral molecule to the corresponding radical anion have been investigated using the Mulliken population analysis. The distribution of the odd electron density in the radical anion was estimated at the different basis sets: STO-3G, 6-31G and 6-31G^**. The ab initio calculations suggest that the quinoid structure is preferred for the radical anion.     

Chlorine nuclear quadrupole resonance study on 1,3-dichloroacetone: dimorphism and temperature dependence of the 35Cl-NQR

Solid 1,3-dichloroacetone, CH₂ClCOCH₂Cl, is dimorphic. The ³⁵Cl-NQR spectra and the X-ray powder patterns are given for both modifications. Phase I shows a single chlorine resonance, whereas phase II (considered to be metastable) gives a four line spectrum. The implications from the NQR spectra with respect to the crystal structures of the two modifications are discussed. The temperature dependence of the ³⁵Cl-NQR frequencies is described by the relationships v^I = 35.9989 ? 16.02 · 10^?1 · T ? 7.350 · 10^?6 · T² + 8.57 · T^?1 (v in MHz, T in K) (Phase I in the range 77 K ? T ? 318 K), and by v₁^II = 36.2968 + 8.19 · 10^?4 · T ? 11.409 · 10^?6 · T² + 13.39 · T^?1, v₂^II = 36.1459 + 5.93 · 10^?4 · T ? 10.447 · 10^?6 · T² + 12.27 · T^?1, v₃^II = 36.0691 + 1.55 · 10^?4 · T ? 9.537 · 10^?6 · T² + 11.72 · T^?1, v₄^II = 35.8244 + 4.42 · 10^?4 · T ? 13.502 · 10^?6 · T² + 17.22 · T^?1, (Phase II in the range 77 K ? T ? 308 K).     

Theoretical study of anion binding to calix[4]pyrrole: the effects of solvent,fluorine substitution,cosolute, and water traces

The binding of different anions to calix[4]pyrrole has been studied by means of molecular dynamics coupled to thermodynamic integration calculations. The effect of different apolar solvents, octafluoro substitution, and the change in binding free energy derived from the presence of cosolute and water traces (the hydrated salt used to introduce the anion in the solution) were examined. Calculations allow us to rationalize the differential binding of ions to calix[4]pyrrole and octafluorocalix[4]pyrrole as well as to predict the behavior in new solvents for which experimental data are not available yet. It is found that both calix[4]pyrrole and octafluorocalix[4]pyrrole have a dramatic preference for F- in the gas phase and pure aprotic solvents, but the situation can change dramatically in protic solvents or in the presence of the hydrated cation which is used as cosolute of the anion. Overall, our results provide interesting clues for a better understanding of the process detected experimentally as "binding".