A theoretical investigation of the interaction between fluorinated dimethyl ethers and molecular chlorine

Halogen bonds have received a great deal of attention in recent years. In this work, the interaction between fluorinated dimethyl ethers (n_F = 0–4) and molecular chlorine has been investigated by the theoretical methods. The two molecules are bonded together by an O···Cl?Cl halogen bond and the interaction energies calculated at the MP2/aug-cc-pVDZ level range between ?15.5 (n_F = 0) and ?6.1 (n_F = 4) kJ mol^?1. The correlations between interaction energies and proton affinity or ionisation potential of the ethers are discussed. The interaction between the molecules results in a small contraction of the CH bond of ethers and an elongation of the Cl?Cl bond. The data are analysed by a natural bond orbital analysis carried out at the wB97XD/6-311++G(d,p) level. The charge transfer from the ethers to Cl₂ is weak, ranges between 0.044 and 0.008 e and occurs mainly to the external Cl atom. The elongation of the Cl?Cl bond is related to the occupation of the σ^*(Cl?Cl) orbital and to the intermolecular hyperconjugation interaction between LP(O) and σ^*(Cl?Cl) orbitals. The interaction between the ethers and chlorine induces an enhancement of the infrared intensity and Raman scattering activity of the ν(Cl?Cl) vibration.     

Comparative studies on CH⋯F− hydrogen bond formation in benzene and exocyclically substituted pentafulvene derivatives

Optimization of CH?F^? complexes of exo‐substituted pentafulvene and meta‐substituted and para‐substituted benzene (substituents: NMe₂, NHMe, NH₂, NHOH, OH, OMe, Br, Cl, F, Me, CCH, CF₃, CONH₂, COMe, CHO, NO₂, NO, and CN) have been performed at the density functional theory level by using Becke hybrid B3LYP functional with 6‐311++G(d,p) basis set. The acidity of the ring CH bond in benzene and fulvene are of similar magnitude, whereas the acidity of the fulvene exocyclic CH₂ group is significantly higher. Various properties based on the H?F^? hydrogen bond (bond length, electron density at BCP, and bond dissociation energy), and the whole molecule (HOMA, sEDA, pEDA, substituent active region, and substituent effect stabilization energy) were analyzed and compared between the fulvene and benzene systems. Sensitivity of the ring CH?F^? hydrogen bond and other substituent dependent properties to substituent effect is substantially greater in fulvene than that of benzene derivatives. In fulvene, the 3‐position is more sensitive than the 4‐position. The sEDA and pEDA parameters used to measure sigma‐electron and pi‐electron excess/deficiency of the ring are mutually correlated for the studied systems. Copyright © 2013 John Wiley & Sons, Ltd.     

A natural bond orbital analysis of aryl‐substituted polyfluorinated carbanions: negative hyperconjugation

Aryl‐substituted polyfluorinated carbanions, ArCHR_f^? where R_f = CF₃ ( 1 ), C₂F₅ ( 2 ), i‐C₃F₇ ( 3 ), and t‐C₄F₉ ( 4 ), were analyzed by means of the natural bond orbital (NBO) theory at the B3LYP/6‐311+G(d,p) computational level. A lone pair NBO at the formal anionic center carbon (Cα) was not found in the Lewis structure. Instead, significant donor/acceptor NBO interactions between π(Cα‐C1) and σ*(Cβ‐F) or σ*(Cβ‐Cγ) were observed for 1 , 2 , 3a (strong electron‐withdrawing substituent, from p‐CF₃ to p‐NO₂), and 4 . Their second‐order donor/acceptor perturbation interaction energy, E(2), values decreased with the increase of the stability of carbanions. A larger E(2) value corresponds to longer Cβ‐F and Cβ‐Cγ bonds and a shorter Cα‐Cβ bond, indicating that the E(2) values can be associated with the negative hyperconjugation of the Cβ‐F and Cβ‐Cγ bonds. In accordance with this, the E(2) values for π(Cα‐C1) → σ*(Cβ‐F) were linearly correlated with the ΔG^o_β‐F values (an empirical measure of β‐fluorine negative hyperconjugation obtained from an increased acidity). In 3b (weak electron‐withdrawing substituents, from H to m‐NO₂) very large E(2) values for LP(Fβ) → π*(Cα‐Cβ) were obtained. This was attributed to the Cβ‐F bond cleavage and the Cα‐Cβ double bond formation in the Lewis structure that is caused by the extremely strong negative hyperconjugation of the Cβ‐F bond.     

The concentration dependence of the proton chemical shift and the deuterium quadrupole coupling parameter for binary solutions of ethanol

Concentration dependent experimental measurements of the ethanol hydroxyl proton chemical shift σ_H for binary solutions were carried out. The solvents used were carbon tetrachloride (CCl₄), benzene, chloroform, acetonitrile, acetone and dimethylsulphoxide (DMSO). The chemical shift values range from 0.69 ppm (relative to TMS) for dilute ethanol (extrapolated to infinite dilution) in CCl₄ to 5.34 ppm for neat liquid ethanol. Ab initio calculations of the ethanol-solvent hydrogen bond energies show a correlation with the values for the chemical shift. The hydrogen bond energies for ethanol-solvent dimers range from 0.63 kcal mol^?1 for ethanol-CCl₄ to 9.34 kcal mol^?1 for ethanol-DMSO. Theoretical calculations show a linear correlation between the deuterium quadrupole coupling parameter XD ^ar d the isotropic proton chemical shift σ_H: X_D(kHz) = 291.48 ? 14.96 σ_H, where σ_H is the proton chemical shift in ppm relative to TMS (R ² = 0.99). Using the concentration dependent chemical shift data and this equation, X_D ia observed to range from 280 kHz for very dilute concentrations in CCl₄, where the primary species is ethanol monomer, to 210 kHz for the neat liquid that is comprised primarily of cyclic pentamers.     

Computational study on structures,thermochemical properties,and bond energies of disulfide oxygen (S–S–O)‐bridged CH3SSOH and CH3SS(=O)H and radicals

Cleavage of disulfide bonds is a common method used in linking peptides to proteins in biochemical reactions. The structures, internal rotor potentials, bond energies, and thermochemical properties (Δ_fH°, S°, and Cp(T)) of the S–S bridge molecules CH₃SSOH and CH₃SS(=O)H and the radicals CH₃SS?=O and C?H₂SSOH that correspond to H‐atom loss are determined by computational chemistry. Structure and thermochemical parameters (S° and Cp(T)) are determined using density functional Becke, three‐parameter, Lee–Yang–Parr (B3LYP)/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p). The enthalpies of formation for stable species are calculated using the total energies at B3LYP/6‐31++G (d, p), B3LYP/6‐311++G (3df, 2p), and the higher level composite CBS–QB3 levels with work reactions that are close to isodesmic in most cases. The enthalpies of formation for CH₃SSOH, CH₃SS(=O)H are ?38.3 and ?16.6 kcal mol^?1, respectively, where the difference is in enthalpy RSO–H versus RS(=O)–H bonding. The C–H bond energy of CH₃SSOH is 99.2 kcal mol^?1, and the O–H bond energy is weaker at 76.9 kcal mol^?1. Cleavage of the weak O–H bond in CH₃SSOH results in an electron rearrangement upon loss of the CH₃SSO–H hydrogen atom; the radical rearranges to form the more stable CH₃SS· = O radical structure. Cleavage of the C–H bond in CH₃SS(=O)H results in an unstable [CH₂SS(=O)H]* intermediate, which decomposes exothermically to lower energy CH₂ = S + HSO. The CH₃SS(=O)–H bond energy is quite weak at 54.8 kcal mol^?1 with the H–C bond estimated at between 91 and 98 kcal mol^?1. Disulfide bond energies for CH₃S–SOH and CH3S–S(=O)H are low: 67.1 and 39.2 kcal mol^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

Proton magnetic resonance of ethane in the liquid and gaseous states

The proton chemical shift of ethane is reported, covering for gaseous ethane the density range 0 to 0·5 g cm^-3 and the temperature range 0 to 110°C, and for liquid ethane from the critical temperature down to -55°C. The results are discussed in terms of the van der Waals interaction term σ _w , using a virial expansion including both binary and ternary collisions. A parallel is drawn between the medium shifts and the equation of state for non-ideal gases. Some comments are made regarding (i) the uniqueness of the parameter B for protons in a C-H bond in non-polar molecules, (ii) the neighbour anisotropy contribution σ _a in molecules such as ethane and ethylene, and (iii) the van der Waals gas-to-liquid medium shift, and its temperature dependence, in larger molecules.     

Na+ ion conductivity and crystallographic cell characterization in the Hf-nasicon system Na1+xHf2SixP3−xO12

We have measured the effect of varying the mobile ion concentration on the sodium ion conductivity in the Hf-Nasicon system, Na_1+xHf₂Si_xP_3-xO₁₂, for 1.4 ? x ? 2.8. The conductivity is greatest for Na_3.2Hf₂Si_2.2 P_0.8O₁₂: σ_25°C = 2.3 × 10^?3 (ω cm)^?1, and σ_250°C = 1.7 × 10^?1 (ω cm)^?1. These values are approximately 50% greater and worse, respectively, than the values reported for the best Zr-Nasicon. We have characterized the variation of lattice parameters with composition and found the behavior to be similar to that of Zr-Nasicon. A small distortion from rhombohedral to monoclinic symmetry occurs for compositions 1.8 ? x ? 2.2.     

Mössbauer sprectroscopic characterization of iron chlorophyllins

The Mössbauer spectra of bis-adducts of pyridine (py) and its derivatives (4-Xpy, where X is CN, CHO, COOCH₃, COCH₃ and CH₃) have revealed that the axial coordination of py and 4-Xpy to iron (III) chlorophyllin gives rise to spontaneous reduction of the central iron (III) ion. A linear correlation between isomer shifts and quadrupole splittings is explained on the basis of the predominant σ-donation from the axial ligand to the central iron ion. The linear dependence of the isomer shifts on the Hammett substituent constants has demonstrated that the larger the isomer shift, the stronger the electron-attracting power of the substituent at the 4-position. The decrease in the quadrupole splitting is ascribed to the relative decrease in the electron density accumulated in the equatorial direction through the σ-donation. The general tendency in the spontaneous reduction of iron (III) chlorophyllin is interpreted in terms of the σ-donor and π-acceptor power of the axial ligands.     

Analysis of the relationship between the electron-capture and electron-loss cross sections for carbon ions

The electron-loss cross sections σ _{i, i + 1} and the electron-capture cross sections σ _{i, i ? 1} for carbon ions with energies of 35–330 keV/nucleon in hydrogen and neon are determined from experimental data. It is demonstrated that, for particle energies which satisfy the condition σ _{i, i + 1} = σ _{i, i ? 1} or σ _{i, i ? 1} = σ _{i ? 1, i} , the average equilibrium ion charge can be evaluated without solving the system of differential equations for charge exchange. The dependence of the average equilibrium ion charge on the ion energy is investigated for carbon ions.     

Predictions on the couplings of f- and ϱ- trajectories to mesons from chiral symmetry

We employ a chiral saturation scheme involving 15, $\text{L = 0,}\text{and}\text{15}\text{, L = 1}$ mesons in a classification according to SU(4) ? O(3) (i.e. the mesonns π, ?, ω, A₁, A₂, f, A₀ (δ), B, D and σ) and calculate all f and ? Regge couplings between these mesons via a matrix version of finite-energy sum rules. In addition the size of exotic exchanges is evaluated and found to be small. The results are compared with experimental numbers and other models as far as available.     

The effect of hydrogen-bonding cooperativity on the strength and properties of σ-hole interactions: an ab initio study

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to investigate the effect of hydrogen-bonding cooperativity on the strength and bonding properties of σ-hole interaction in linear FCl???(NCH)_n=2–5, FHS???(NCH)_n=2–5, FH₂P???(NCH)_n=2–5 and FH₃Si???(NCH)_n=2–5 clusters. It is found that the cooperative effects in the hydrogen-bonding tend to strengthen the σ-hole interaction. However, these effects are almost saturated in the larger clusters (n > 5). For a given cluster, the amount of bond contraction in FCl???(NCH)_n is more important than other systems. A nice linear relationship is found between the σ-hole bond energies and absolute ¹⁵N chemical shieldings or spin–spin coupling constants across the σ-hole bond.     

多重散射团簇方法对吸附系统SO2/Ag(110)的理论分析

利用多重散射团簇方法(MSC)对吸附系统SO₂/Ag(110)的S原子K边X射线吸收精细结构谱(NEXAFS)作了理论分析.研究表明,覆盖度为0.5时,吸附的SO₂的S—O键长比气体状态时增长了(0.014±0.006)nm,OSO键角减小了15°±5°;SO₂分子的S原子处于芯位,但两个O原子处于不对称的位置;分子平面与(110)的夹角约为52°,同时分子平面相对衬底表面法线有一小角度的倾斜.MSC计算证实了该吸附系统存在一介于π^{关键词： X射线吸收精细结构 2/Ag(110)')" href="#">吸附系统SO₂/Ag(110) 多重散射团簇方法}     

Photoelectron spectroscopy of molecular systems and quantum-chemical calculations in terms of the density functional theory: Iron π complexes L-Fe(CO)3

The HeI and NeI photoelectron spectra of irontricarboniyl complexes with cyclic diene ligands—αmethylstyrene, orthoquinodimethane, and cyclooctatetraene—were obtained. The results of quantum-chemical calculations of the molecules of these compounds in the approximation of the density functional theory (B3LYP/6-31G*) are presented. It is shown that this approximation describes well the excited ionic states of the π complexes under study. The relative ionization cross sections σ_π and σ_3d , which characterize the probability of removal of electrons from the molecular π-ligand and 3d-metal orbitals, are estimated. The mechanism of the selective coordination of the Fe(CO)₃ groups to corresponding organic ligands is discussed. The energies of the L-Fe(CO)₃ chemical bond are calculated.     

Static and high-frequency hole transport in <Emphasis Type="Italic">p</Emphasis>-Si/SiGe heterostructures in the extreme quantum limit

Complex high-frequency (HF), σ^AC = σ₁ ? iσ₂, and static, σ^DC, conductivities, as well as current-voltage characteristics, have been measured in p-Si/SiGe heterostructures with a low hole density (p = 8.2 × 10¹⁰ cm^?2) at temperatures T = 0.3–4.2 K in the ultraquantum limit, when the filling factor is v < 1. In order to determine the components of the HF conductivity, the acoustic contactless method in the “hybrid configuration” is used, when the surface acoustic wave propagates on the surface of the LiNbO₃ piezoelectric and the heterostructure is pressed to the surface by a spring. The conductivities σ₁ and σ₂ are determined from the damping and velocity of the surface acoustic waves that are measured simultaneously with varying the magnetic field. The revealed HF conductivity features—σ₁ ? |σ₂|, the negative sign of σ₂, the threshold behavior of the current-voltage characteristic, and the dependence I ∝ exp(-A/V ^0.3) in the subthreshold region—indicate the formation of a pinned Wigner crystal (glass) in the ultraquantum limit (T = 0.3–0.8 K, B > 14 T).     

Natural bond orbital (NBO) analysis of the angular group induced bond alternation (AGIBA) substituent effect

The geometries, natural charges, and resonance structures of 11 monosubstituted benzene derivatives were analyzed at the B3LYP/6‐311++G(d,p) and HF/6‐311++G(d, p) levels of theory. The following angular substituents were chosen: OCH₃, CH₂CH₃, OH, SH, NHCH₃, NHNH₂, N?O, CH?CH₂, N?CH₂, N?NH, and CHO. The analysis of resonance structures was performed by using two different methodologies: harmonic oscillator stabilization energies (HOSE) and natural resonance theory (NRT). Also, the natural bond orbital (NBO) donor–acceptor stabilization energies for different resonance structures were calculated. We found that for all the substituents, the purely geometric resonance stabilization parameter (HOSE) is linearly correlated with quantum chemically derived resonance structure weight (NRT) of a given structure. Also, the calculations provide qualitative support for the earlier assumption of a through space angular group induced bond alternation (AGIBA) effect. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical investigations on the g factors and local structures for Cu2+ in the ZnX (X= O,S and Se) nanocrystals

ABSTRACT

The g factors and local structures for Cu²⁺ in the ZnX (X = O, S and Se) nanocrystals at room temperature are theoretically investigated by the perturbation calculations for a tetragonally distorted tetrahedral 3d⁹ cluster in a consistent way, and the isotropic g factor is predicted for the ZnS:Cu²⁺ nanocrystals at room temperature. The bond angles θ between the four equivalent Cu²⁺?X^2? bonds and the C₄ axis are found to be about 1.26°, 1.24° and 1.07°, respectively, larger in the ZnO, ZnS and ZnSe nanocrystals than that (θ₀ ≈ 54.74°) for an ideal tetrahedron, inducing tetragonally compressed tetrahedra. The declining tendency (ZnO > ZnS > ZnSe) of the tetragonal angular distortion Δθ (= θ ? θ₀) can be ascribed to the decreasing strength of the dynamic Jahn–Teller effect via the vibration interactions of the [CuX₄]^6? groups due to the weakening Cu²⁺?X^2? bonding. The isotropic g factors are attributable to the appropriate Δθ due to the dynamic Jahn–Teller effect and the internal stress. The slightly increasing (ZnO < ZnS < ZnSe) g factors can be illustrated by the declining cubic field parameter Dq, angular distortion Δθ and covalency factor N of the systems.     

Classical trajectory calculations for state-resolved Penning ionisation reactions of polycyclic aromatic hydrocarbon C10H8 in collision with He*(23S)

ABSTRACT

The reaction dynamics of Penning ionisation of a polycyclic aromatic hydrocarbon (PAH), naphthalene C₁₀H₈, in collision with the metastable He*(2³S) atom is studied by classical trajectory calculations using an approximate interaction potential energy surface between He* and the molecule, which is constructed based on ab initio calculations for the isovalent Li?+?C₁₀H₈ system. The ionisation width (rate) around the molecular surface are obtained from overlap integrals of the He 1s orbital and the molecular orbital. The calculated collision energy dependences of partial Penning ionisation cross sections (CEDPICS) in the range 50–500?meV at 300?K have reproduced the experimental results semi-quantitatively. The opacity functions, which represent the reaction probability with respect to the impact parameter b, are discussed in connection with collision energy, interaction with He* and the exterior electron density of molecular orbitals. They indicate that the collisional ionisations of C₁₀H₈ can be classified into three types: π electron ionisations with negative collision energy dependences which are predominantly determined by attractive interaction with He*; σ orbitals ionisations of the hardcore type; σ orbital ionisations which reflect interaction potentials around CH bonds. The critical impact parameters b_c become larger with increasing collision energy due to the centrifugal barrier.     

Synthesis,crystal structure and dielectric properties of C6H18N2SbCl5

The result of the X‐ray diffraction, differential scanning calorimetry and dielectric studies on a new crystal material C₆H₁₈N₂SbCl₅ is presented. The new organic–inorganic compound has been synthesized and characterized by the X‐ray diffraction method at 296(2) K. It crystallizes in the monoclinic P21/n space group. The cell dimensions are: a = 5.8617(1) Å, b = 15.7069(2) Å, c = 16.6693(2) Å, β = 97.627(1)° and Z = 4. The crystal structure consists of a discrete ionic layer of (C₆H₁₈N₂)²⁺ cations and [SbCl₅]^2? anions linked via simple and bifurcated N―H · · · Cl hydrogen bonds. DSC analysis shows that this compound undergoes a phase transition at about (384 ± 2) K. AC and DC conductivities, complex dielectric permittivity ε*(ω) and complex electrical modulus M*(ω) were respectively studied as temperature and frequency functions. The combined data support each other and confirm the existence of a structural phase transition at about 384 K. Moreover, the temperature dependence of the DC conductivity and relaxation frequency followed the Arrhenius relation. The frequency dependence of the real part of the AC conductivity in both phases follows the Jonscher's universal dynamic law: . The behavior of s(T) with temperature suggests that the hopping over barrier model (CBH) and the small polaron tunneling mechanism (SPTM) prevail in phases I and II, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Mechanism of nucleophilic substitutions at phenacyl bromides with pyridines. A computational study of intermediate and transition state

DFT computations have been performed on nucleophilic substitutions of phenacyl bromides with pyridines to investigate the mechanism of the reaction. In contrast with earlier suppositions, tetrahedral intermediate is not formed by the addition of pyridine on the C?O group of phenacyl bromide, because the total energy of the reacting species increases continuously, when the distance between the N and C(?O) atoms of reactants is shorter than 2.7 Å. At a greater distance, however, a bridged complex of the reactants is observed, in which the N atom of pyridine is slightly closer to the C atom of the C?O, than to the C atom of the CH₂Br group of phenacyl bromide, the distances are 2.87 and 3.05 Å, respectively. The attractive forces between the oppositely polarized N and C(?O) atoms in the complex decrease the free energy of activation of the S_N2 attack of pyridine at the CH₂Br group. The calculated structural parameters of the S_N2 transition states (TS) indicate, that earlier TSs are formed when the pyridine nucleophile bears electron‐donating (e‐d) groups, while electron‐withdrawing (e‐w) groups on phenacyl bromide substrate increase the tightness of the TS. Free energies of activation computed for the S_N2 substitution agree well with the data calculated from the results of kinetic experiments and correlate with the σ_Py substituent constants, derived for pyridines, and with the Hammett σ constants, when the substituents (4‐MeO‐4‐NO₂) are varied on the pyridine or on the phenacyl bromide reactants. Copyright © 2008 John Wiley & Sons, Ltd.     

Dependence of the GaAs (110) surface electronic state dispersion curves on the surface relaxation angle

The surface state dispersion curves E($\text{k}$) of the dangling bond states near the fundamental band gap, C₃ and A₅, are computed for both the established θ?27° model and the recently proposed θ?7° model of the (110) surface relaxation of GaAs, where θ is the surface bond rotation angle. The two models produce surface state dispersion curves that are similar to one another and to the data.