Conformational Properties of (Z,Z)-, (E,Z)-, and (E,E)-Cycloocta-1,4-dienes

Summary.  Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and the MP2/6-31G^*//HF/6-31G^* level for a single point total energy calculation are reported for (Z,Z)-, (E,Z)-, and (E,E)-cycloocta-1,4-dienes. The C ₂-symmetric twist-boat conformation of (Z,Z)-cycloocta-1,4-diene was calculated to be by 3.6 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form; the calculated energy barrier for ring inversion of the twist-boat conformation via the C _S-symmetric boat-boat geometry is 19.1 kJ·mol⁻¹. Interconversion between twist-boat and boat-chair conformations takes place via a half-chair (C ₁) transition state which is 43.5 kJ·mol⁻¹ above the twist-boat form. The unsymmetrical twist-boat-chair conformation of (E,Z)-cycloocta-1,4-diene was calculated to be by 18.7 kJ·mol⁻¹ more stable than the unsymmetrical boat-chair form. The calculated energy barrier for the interconversion of twist-boat-chair and boat-chair is 69.5 kJ·mol⁻¹, whereas the barrier for swiveling of the trans-double bond through the bridge is 172.6 kJ·mol⁻¹. The C _S symmetric crown conformation of the parallel family of (E,E)-cycloocta-1,4-diene was calculated to be by 16.5 kJ·mol⁻¹ more stable than the C _S-symmetric boat-chair form. Interconversion of crown and boat-chair takes place via a chair (C _S) transition state which is 37.2 kJ·mol⁻¹ above the crown conformation. The axial- symmetrical twist geometry of the crossed family of (E,E)-cycloocta-1,4-diene is 5.9 kJ·mol⁻¹ less stable than the crown conformation. Corresponding author. E-mail: isayavar@yahoo.com Received March 25, 2002; accepted April 3, 2002     

Accurate values for the nonrelativistic energies of the lowest singlet and triplet S-states of the4He-Isotop

Accurate lower and upper bounds for the nonrelativistic lowest energies¹ E ₀ and³ E ₀ of the singlet and triplet-system of the⁴He-Isotop are calculated with the linearized method of variance minimization. The same was done for¹ E ₁ the energy of the first excitedS-state 2¹ S. The results especially for¹ E ₀ and³ E ₀ in a.u. are −2.9033076997₅ ≤¹ E ₀ ≤ −2.9033076921₈ −2.1749324263₇ ≤³ E ₀ ≤ −2.1749324245₉ i.e. the values are determined with an absolute error smaller than 0.00167 cm⁻¹ for¹ E ₀ and 0.00039 cm⁻¹ for³ E ₀.     

Electrochemical behavior and parameters of hydrofullerene C60H36

Electrochemistry of hydrofullerene C₆₀H₃₆ was studied by cyclic voltammetry in THF and CH₂Cl₂ in the −47–14 °C temperature range. Hydrofullerene undergoes reversible one-electron reduction to form a radical anion in THF (E ⁰=−3.18 V (Fc⁰/Fc⁺), Fc=ferrocene) and irreversible one-electron oxidation in CH₂Cl₂ (E _p ^a =1.22 V (Fc⁰/Fc⁺)). The reduction potential was used to estimate electron affinity of hydrofullerene as EA=−0.33 eV. It was suggested that C₆₀H₃₆ is an isomer withT-symmetry in which 12 double bonds form four isolated benzenoid rings located in vertices of an imaginary inscribed tetrahedron on the molecular surface. For hydrofullerene, the “electrochemical gap” is an analog of the energy gap (HOMO−LUMO), equal to (E ^Ox−E ^Red)=4.4 V, and indicates that C₆₀H₃₆ is a sufficiently “hard” molecule with a low reactivity in redox reactions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2083–2087, November, 1999.     

Physical factors determining the activation energy of alkyl radical addition to unsaturated compounds

A parabolic model of the transition state is used for the analysis of experimental data (rate constants and activation energies) for reactions of addition of alkyl and phenyl radicals to multiple bonds of unsaturated compounds. The parameters describing the activation energy as a function of the enthalpy of the reactions were calculated from the experimental data. The activation energy depends also on the strength of the forming C−C bond, the presence of π-bonds in the α-position near the attacked C=C bond and the presence of polar groups in the monomer and radical. The empirical dependence of the activation energy of a thermoneutral addition reactionE _e0 on the dissociation energyD _e of the forming C−C bond was obtained:E _e0=(5.95±0.06)·10⁻⁴ D _e ² kJ mol⁻¹, indicating the important role of triplet repulsion in the formation of the transition state of radical addition. The contribution of the polar interaction to the activation energy of addition of polar radicals to polar monomers was calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 445–450, March, 1999.     

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) initiated by Ce(CIO4)3 in the excited state

Photocatalytic decomposition of dispiro(diadamantane-1,2-dioxetane) (1) to adamantanone (2) initiated by Ce(ClO₄)₃ in the excited state in the MeCN−CHCl₃ (2∶1) mixture was studied. The bimolecular rate constants of quenchingk _q were determined from the kinetics of quenching of Ce^3+* by dioxetane at different temperatures. The Arrhenius parameters of the quenching were calculated from the temperature dependence ofk _q:E _a=3.2±0.3 kcal mol⁻¹ and logA=11.6±6. The quantum yields of photolysis of 1 depending on its concentration and the rate constant of the chemical reaction of Ce^3+* with 1 were determined. The latter coincides withk _q:k _ch=(2.6±0.3)·10⁹ L mol⁻¹ s⁻¹ (T=298 K). The fact that the maximum quantum yield of decomposition of dioxetane is equal to 1 indicates the absence of physical quenching of Ce^3+* with 1. Nonradiative deactivation of Ce^3+* in solutions of MeCN and in MeCN−CHCl₃ mixtures was studied. It is caused by the replacement of H₂O molecules in the nearest coordination surroundings of Ce³⁺ by solvent molecules and reversible transfer of an electron to the ligand. The activation parameters of the nonradiative deactivation of Ce^+* were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 724–729, April, 1997.     

Water splitting in low-temperature ac plasmas at atmospheric pressure

Plasma-induced water splitting at atmospheric pressure has been studied with a novel fan-type Pt reactor and several tubular-type reactors: an all-quartz reactor, a glass reactor, and three metal reactors with Pt. Ni, and Fe as electrodes. Reaction products have been analyzed by using GC (gas chromatography) and Q-MS (quadrupole mass spectrometry). Optical emission spectroscopic studies of the process have been carried out by employing a CCD (charge-coupled device) detector. Water splitting with tubular quartz and glass reactors is probably non-catalytic. However, a heterogeneous catalytic function of surface of metal electrodes has been observed. The variation of hydrogen yield (Y_H) and energy efficiency (E_e) with operational parameters such as input voltages (U_in), flow rates of carrier gas (F_He), and concentrations of water (C_W) has been examined. Plasma-induced water splitting can be described with a kinetic equation of-dC_w/dt = kC_W ^0.2. The rate constants at 3.25 kV are 2.8 × 10⁻⁴, 3.5 × 10⁻³, and 3.4 × 10⁻² mol^0.8L^−0.8 min⁻¹ for tubular glass reactor, a tubular Pt reactor, and a fan-type Pt reactor, respectively. A CSTR (continuous-stirred tank reactor) and PFR (piston-flow reactor) model have been applied to a fan-type reactor and tubular reactor, respectively. A mechanism on the basis of optical emission spectroscopic data has been obtained comprising the energy transfer from excited carrier gas species to water molecules, which split via radicals of HO^·, O^·, and H^· to form H₂ and O₂. The fan-type Pt reactors exhibit highest activity and energy efficiency among the reactors tested. Higher yields of hydrogen are achieved at higher input voltages, low flow rates, and low concentrations of water (Y_H = 78 % at U_in of 3.75 kV, F_He of 20 mL/min, and C_W of 0.86 %). The energy efficiency exhibits an opposite trend (E_e = 6.1 % at U_in of 1.25 kV, F_He of 60 mL/min and C_W of 3.1 %).     

Thermal behavior and thermal safety on 3,3-dinitroazetidinium salt of perchloric acid

3,3-Dinitroazetidinium (DNAZ) salt of perchloric acid (DNAZ·HClO₄) was prepared, it was characterized by the elemental analysis, IR, NMR, and a X-ray diffractometer. The thermal behavior and decomposition reaction kinetics of DNAZ·HClO₄ were investigated under a non-isothermal condition by DSC and TG/DTG techniques. The results show that the thermal decomposition process of DNAZ·HClO₄ has two mass loss stages. The kinetic model function in differential form, the value of apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of DNAZ·HClO₄ are f(α) = (1 − α)⁻¹/2, 156.47 kJ mol⁻¹, and 10^15.12 s⁻¹, respectively. The critical temperature of thermal explosion is 188.5 °C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠of this reaction are 42.26 J mol⁻¹ K⁻¹, 154.44 kJ mol⁻¹, and 135.42 kJ mol⁻¹, respectively. The specific heat capacity of DNAZ·HClO₄ was determined with a continuous C _p mode of microcalorimeter. Using the relationship between C _p and T and the thermal decomposition parameters, the time of the thermal decomposition from initiation to thermal explosion (adiabatic time-to-explosion) was evaluated as 14.2 s.     

Non-isothermal crystallization of K<Subscript>2</Subscript>O·TiO<Subscript>2</Subscript>·3GeO<Subscript>2</Subscript> glass

The crystallization of K₂O·TiO₂·3GeO₂ glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization was dominant and an activation energy of crystal growth of E _a,s=327±50 kJ mol⁻¹ was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes >0.45 mm, volume crystallization dominated with spherulitic morphology of the crystals growth and E _a,v=359±64 kJ mol⁻¹ was calculated.     

Magnetic properties of fullerene salts containing d- and f-metal cations (Co2+, Ni2+, Fe2+, Mn2+, Eu2+, Cd2+). Specific features of the interaction between C60·? and the metal cations

The interaction between the radical anions C₆₀ ^·− and divalent d- and f-metal (Co, Fe, Ni, Mn, Eu, Cd) cations in DMF and acetonitrile-benzonitrile (AN-BN) mixture was studied. Black solid polycrystalline salts (C₆₀ ^·−)₂{(M²⁺)(DMF) _x } (x = 2.4–4, 1–6) containing the radical anions C₆₀ ^·− and metal(ii) cations solvated by DMF were prepared for the first time and their optical and magnetic properties were studied. The salts containing Co²⁺, Fe²⁺, and Ni²⁺ are characterized by antiferromagnetic interactions between the radical anions C₆₀ ^·−, which result in unusually large broadening of the EPR signal of C₆₀ ^·− upon lowering the temperature (from 5.55–12.6 mT at room temperature to 35–40 mT at 6 K for Co²⁺ and Ni²⁺). The salts containing Mn²⁺ and Eu²⁺ form diamagnetic dimers (C₆₀ ⁻)₂, which causes a jumpwise decrease in the magnetic moment of the complexes and disappearance of the EPR signal of C₆₀ ^·− in the temperature range 210–130 K. A feature of salt 6 is magnetic isolation of the radical anions C₆₀ ^·− due to the presence of diamagnetic cation Cd²⁺. The salts prepared are unstable in air and decompose in o-dichlorobenzene or AN. Reactions of C₆₀ ^·− with metal(ii) cations in AN-BN mixture result in decomposition products of the salts that contain neutral fullerene dimers and metals solvated by BN. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1909–1919, September, 2008.     

Calculation of spectral characteristics of water clusters upon interaction with oxygen molecules and bromine ions

Interactions of (Br⁻) _i (H₂O)_50−i clusters (0 ≤ i ≤ 6) with molecular oxygen is studied by the molecular dynamics method using flexible molecule model. Values of real and imaginary parts of permittivity decrease in the 0 ≤ ω ≤ 3500 cm⁻¹ frequency range with increasing number of bromine ions in a cluster. The ability of cluster to absorb IR radiation decreases, whereas the reflectance and Raman light scattering remains nearly unchanged. An increase in the content of Br⁻ ions in the cluster lowers the power of emitted IR radiation and decreases the amount of active electrons participating in the interaction with IR radiation. However, when the concentration of Brions becomes substantially higher (at i = 5 and 6), the values of emitted power and the number of active electrons are restored to the values that are typical for water cluster in the absence of Br⁻ ions. At i ≥ 3, repelling Br⁻ ions acquire kinetic energy, which is sufficient to remove molecular oxygen from the system.     

Thermodynamic Properties of Hydrofullerene C60H36 from 5 to 340 K

The temperature dependence of the molar heat capacity (C⁰ _p) of hydrofullerene C₆₀H₃₆ between 5 and 340 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. The experimental data were used for the calculation of the thermodynamic functions of the compound in the range 0 to340 K. It was found that at T=298.15 K and p=101.325 kPa C⁰ _p (298.15)=690.0 J K⁻¹ mol⁻¹,H^o(298.15)−H^o(0)= 84.94 kJ mol⁻¹,S^o(298.15)=506.8 J K⁻¹ mol⁻¹, G^o(298.15)−H^o(0)= −66.17 kJ mol⁻¹. The standard entropy of formation of hydrofullerene C₆₀H₃₆ and the entropy of reaction of its formation by hydrogenation of fullerene C₆₀ with hydrogen were estimated and at T=298.15 K they were Δ_fS^o= −2188.4 J K⁻¹ mol⁻¹ and Δ_rS^o= −2270.5 J K⁻¹mol⁻¹, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Effect of Different Aqueous Ionic Media on the Acid-Base Properties of Some Open Chain Polyamines

Acid-base properties of some open-chain polyamines (ethylenediamine, diethylenetriamine, triethylenetetramine, spermine, tetraethylenepentamine and pentaethylenehexamine) were studied at different ionic strengths in different aqueous ionic media at 25 °C. Measured were: (i) the protonation constants of triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine from potentiometric measurements [0 ≤I≤2.5 mol⋅L⁻¹ in NaCl and (CH₃)₄NCl)]; and (ii) protonation enthalpies of ethylenediamine, diethylenetriamine, and spermine from calorimetric measurements [NaCl: 0≤I≤1 mol⋅kg⁻¹ for ethylenediamine, diethylenetriamine, 0 ≤I≤2 mol⋅kg⁻¹ for spermine; (C₂H₅)₄NI: 0≤I≤1 mol⋅kg⁻¹; (CH₃)₄NCl: 0 ≤I≤2.5 mol⋅kg⁻¹ only for diethylenetriamine]. Previously published protonation data for these polyamines in aqueous NaCl, (CH₃)₄NCl and (C₂H₅)₄NI, were also examined. The general trends for the Gibbs energy and entropic contributions are, for ΔG: NaCl>(CH₃)₄NCl>(C₂H₅)₄NI, and for TΔS: (C₂H₅)₄NI>(CH₃)₄NCl>NaCl. This trend is more pronounced for the first protonation step. The dependences of these quantities on ionic strength were modeled with the SIT (Specific ion Interaction Theory) equations, and differences found among the different media were interpreted in terms of weak complex formation.     

Anisotropy in the physical properties of UNiGa under high pressure

The linear thermal expansion, compressibility and magnetostriction of UNiGa have been measured under high pressure. Huge anisotropic behaviors are observed in these physical quantities. The linear thermal expansion coefficients are α _a ∼ 16·10⁻⁶ K⁻¹ along thea-axis anda _c ∼5·10⁻⁶ K⁻¹ along thec-axis, and the linear compressibilities at room temperature are κ _a ∼ 3.6·10⁻³ GPa⁻¹ and κ _c ∼ 1.7·10⁻³ GPa⁻¹ alonga-axis andc-axes, respectively. UNiGa orders antiferromagnetically belowT _N=39 K and shows a metamagnetic transition at 4.2 K in magnetic fieldB _C=1 T. It is found thatT _N decreases andB _C increases with increasing pressure.     

Thermal behavior study and decomposition kinetics of salbutamol under isothermal and non-isothermal conditions

The thermal decomposition of salbutamol (β₂ — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage of the thermal decomposition process. For isothermal experiments the average values were E _act=130 kJ mol⁻¹ (for standard sample) and E _act=252 kJ mol⁻¹ (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min⁻¹). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min⁻¹). The calculated values were E _act=134 kJ mol⁻¹ (for standard sample) and E _act=139 kJ mol⁻¹ (for pharmaceutical sample).     

Generation of fullerenyl radicals and chemiluminescence in the (C<Subscript>60</Subscript>—R<Subscript>3</Subscript>Al)—O<Subscript>2</Subscript> system

Fullerenyl radicals (FR) RC₆₀ ^· and chemiluminescence (CL) are generated in the presence of O₂ in C₆₀—R₃Al (R = Et, Buⁱ) solutions in toluene (T = 298 K). The FR are formed due to the addition of the R^· radical, which is an intermediate of R₃Al autooxidation, to C₆₀. Mass spectroscopy and HPLC were used to identify Et_nC₆₀H_m (n, m = 1–6), Et_pC₆₀ (p = 2–6), and dimer EtC₆₀C₆₀Et as stable products of FR transformations. As found by ESR, the EtC₆₀ ^· radical (g = 2.0037) is also generated by photolysis of solutions obtained after interaction in the (C₆₀— R₃Al)—O₂ system. In the presence of dioxygen, the FR is not oxidized but yields complexes with O₂, which appear as broadening of the ESR signals. Chemiluminescence arising in the (C₆₀—R₃Al)—O₂ system is much brighter (I _max = 1.86·10⁸ photon s⁻¹ mL⁻¹) than the known background CL (I _max = 6.0·10⁶ photon s⁻¹ mL⁻¹) for the autooxidation of R₃Al and is localized in a longer-wavelength spectral region (λ_max = 617 and 664 nm). This CL is generated as a result of energy transfer from the primary emitter ³CH₃CHO* to the products of FR transformation: R_nC₆₀H_m, R_pC₆₀, and EtC₆₀C₆₀Et. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–213, February, 2007.     

Fullerene C<Subscript>60</Subscript> as a superefficient quencher of singlet exited states of polycyclic aromatic hydrocarbons

Quenching of fluorescence of polycyclic aromatic hydrocarbons (PAH), namely, naphthalene, anthracene, 9,10-diphenylanthracene, 9,10-dibromoanthracene by C₆₀ fullerene in ethylbenzene at 293 K was found and investigated. The phenomenon is characterized by abnormally high values of bimolecular rate constants for quenching (k _bim = (0.18–6.78)·10¹² L mol⁻¹ s⁻¹) determined from the Stern—Volmer dependence of the PAH fluorescence intensity on the C₆₀ concentration and occurs through the inductive-resonance (dominant channel) and exchange-resonance (minor channel) energy transfer from ¹PAH* to C₆₀. The overlap integrals of the PAH fluorescence spectra with the C₆₀ absorption spectrum and the critical energy transfer distances were calculated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 432–436, March, 2007.     

Extraction and DFT study on the complexation of the cesium cation with a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs⁺(aq) + A⁻(aq) + 1(nb) ⇆ 1·Cs⁺(nb) + A⁻ (nb) taking part in the two-phase water–nitrobenzene system (A⁻ = picrate, 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, A⁻) = 2.8 ± 0.1. Further, the stability constant of the hexaarylbenzene-based receptor·Cs⁺ complex (abbrev. 1·Cs⁺) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Cs⁺) = 4.7 ± 0.1. By using quantum mechanical DFT calculations, the most probable structure of the 1·Cs⁺ complex species was solved. In this complex having C ₃ symmetry, the cation Cs⁺ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation–π interaction. Finally, the calculated binding energy of the resulting complex 1·Cs⁺ is −220.0 kJ/mol, confirming relatively high stability of the considered cationic complex species.     

Fullerene complexes with bis(η6-hexamethylbenzene)chromium, hexamethylbenzene, and hexaethylbenzene

The [60]fulleride of bis(η-hexamethylbenzene)chromium(I) [(η⁶-C₆Me₆)₂Cr]^⋅+[C₆₀]^⋅−, and the complexes C₆₀·C₆Me₆ and C₆₀·C₆Et₆ were synthesized. Thermal decomposition of [(η⁶-C₆Me₆)₂Cr]^⋅+[C₆₀]^⋅− was studied. The molecular structures of C₆₀·C₆Me₆ and C₆₀·C₆Et₆ were determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 220—224, February, 2006.     

Sorption behavior of Sn(II) onto Haro river sand from aqueous acidic solutions

The sorption behavior of Sn(II) onto Haro river sand has been examined with respect to nature of electrolyte, agitation time, dosage of sorbent and concentration of sorbate. Maximum sorption (95.5%) has been achieved from 0.034M hydrochloric acid solution after equilibrating sorbate (2·10⁻⁵M) and sorbent (50 mg) for 120 minutes at aV/W ratio of 90 cm³·g⁻¹. The kinetic data have been subjected to Morris-Weber and Lagergren equations. The kinetics of sorption proceeds a two stage process consisting of a relatively slow initial uptake followed by a much rapid increase in the sorption. The rate constant of intraparticle transport, K_d, comes out to be 8.75·10⁻⁸ mol·g⁻¹·min^−1/2 and the first order rate constant for sorption is 0.0416 min⁻¹. The sorption data of Sn(II) onto Haro river sand followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) type isotherms. The Langmuir constant,Q, related to sorption capacity and,b, related to sorption energy are computed to be 10.6±1.1 μmol·g⁻¹ and 1123±137 dm³·mol⁻¹, respectively. The D-R isotherm yields the values ofC _m=348±151 μmol·g⁻¹ and β=−0.01044±0.0008 mol²·kJ⁻² and ofE=6.9±0.3 kJ·mol⁻¹. In all three isotherms correlation factor (γ) is ≥0.99. The influence of common anions and cations on the sorption has been investigated. Zn(II), Mg(II), oxalate, Pb(II), Mn(II) and tartrate reduce the sorption significantly whereas Fe(II) causes substantial increase in the sorption. It is essential that all ions causing a decrease in the sorption of Sn(II) must be absent from the sorptive solution otherwise low sorption yields would result.