Butterfly Methanes: Designing a Novel Class of anti-van′t Hoff Carbons

Among different possible non-classical structures, the stabilization of half-planar tetracoordinate carbon conformation is believed to be the most difficult one. Herein, we designed three types of half-planar tetracoordinate carbon compounds computationally by employing hybrid stabilization effects of substituents. The axial hydrogens of unstable half-planar methane are substituted with π-acceptor and σ-donor substituents such as −BH₂, −Li and the equatorial substituents selected are a combination of electropositive atoms (σ-donors)/electronegative atoms (σ-acceptors and π-donors). To establish the stabilization factors, we conducted a detailed study on vibrational frequency analysis, molecular orbital analysis (including Natural Bond Orbitals) and electrostatic potential (ESP) analysis of optimized molecular geometries using density functional theory.     

Kinetics of one-electron oxidation by the ClO radical

Pulse radiolysis studies were carried out to determine the rate constants for reactions of ClO radicals in aqueous solution. These radicals were produced by the reaction of OH with hypochlorite ions in N₂O saturated solutions. The rate constants for their reactions with several compounds were determined by following the build up of the product radical absorption and in several cases by competition kinetics. ClO was found to be a powerful oxidant which reacts very rapidly with phenoxide ions to form phenoxyl radicals and with dimethoxybenzenes to form the cation radicals (k = 7 × 10⁸ −2 × 10⁹ M^-1 s^-1). ClO also oxidizes ClO^-₂ and N^-₃ ions rapidly (9.4 × 10⁸ and 2.5 × 10⁸ M^-1 s^-1, respectively), but its reactions with formate and benzoate ions were too slow to measure. ClO does not oxidize carbonate but the CO^-₃ radical reacts with ClO^- slowly (k = 5.1 × 10⁵ M^-1 s^-1).     

A re-examination of the decay kinetics of pulse radiolytically generated Br-2 radicals in aqueous solution

The decay of Br^-₂ in Ar-purged or N₂O-saturated aqueous solutions of KBr (0.01-1.0 M) in the pH range 1–7 has been re-examined using the techniques of pulse radiolysis and computer simulation. The dependence of the rate constant for the intrinsic decay of Br^-₂ on ionic strength (controlled by KBr) has been established; the values of k (Br^-₂ + Br^-₂) are (1.9 ± 0.1) × 10⁹, (2.2 ± 0.3) × 10⁹ and (2.4 ± 0.3) × 10⁹ M^-1 s^-1 in the presence of 0.01, 0.1 and 1.0 M KBr, respectively, independent of pH between 2 and 7. The computer simulation of the decay of Br^-₂ has also generated, for the latter species, ϵ = 10,000 ± 700 M^-1 cm^-1 at λ_max = 360 nm; this value has been calculated without making any assumption concerning G(Br^-₂). For the reduction of Br^-₂ by H atoms, a value of k (H + Br^-₂) = (1.4 ± 0.3) × 10¹⁰ M^-1 s^-1 has been obtained in the presence of 0.01-1.0 M KBr, independent of pH between 1–4. For the reduction of Br^-₂ by e^-_aq at pH 7 (10^-3 M phosphates) and μ = 0.1, a value of k (Br^-₂ + e^-_aq = (1.1 ± 0.2) × 10¹⁰ M^-1 s^-1 has been obtained.     

离子对生成反应的LCAC-SW量子散射理论研究＊

LCAC-SW method has been extended to study the reaction dynamics for ion-pair formation processes.M+X₂M⁺+X^-₂ reaction system involves two potential energy surfaces,i.e.,the covalence state(M+X₂) and the ionic state(M⁺+X^-₂) and their crossing effect.The working equations for calculating state-to-state probability have been derived based on the above two-state model.The selected-state reaction probabilities of collinear ion-pair formation process M+I₂M⁺+I^-₂(M=Na,K,Cs) on Aten-Lanting-Los two-state potential energy surface have been calculated.The results show that the reaction probabilities are of resonance effect.     

碱土金属掺杂对钴基尖晶石复合金属氧化物催化分解N_2O性能的影响

采用共沉淀法制备碱土金属掺杂的钴基尖晶石型复合金属氧化物M_xCo_(3-x)O_4(M=Mg、Ca、Sr、Ba;x=0、0.1、0.3、0.5、0.7、0.9)催化剂,使用XRD、SEM、氮吸附、H_2-TPR、O_2-TPD-M S和XPS等技术对催化剂进行表征,并在固定床微型反应器中评价了M_xCo_(3-x)O_4催化剂催化分解N_2O的活性,研究了碱土金属掺杂对其催化性能的影响。结果表明,碱土金属掺杂后,M_(x )Co_(3-x)O_4催化剂颗粒粒径减小,比表面积增大,表面吸附氧和Co~(2+)数量增加,氧化还原性能增强;在反应气组成为0.68%N_2O,3%O_2,Ar为平衡气的条件下,碱土金属锶掺杂、掺杂量x为0.7时,Sr_(0.7)Co_(2.3)O_4的N_2O分解催化活性最高,N_2O转化率为10%和95%时所需的温度分别为312和451℃。     

Interaction of tris(2,2′-bipyrazine)ruthenium(2+) ion with radiolytically-generated radicals in aqueous solution. Reactivity of Ru(bpz)+3 toward electron relays

The one-electron reduction of Ru(bpz)²⁺₃ by (CH₃)₂ḢOH is rapid (k = 3.5 × 10⁹ M^-1 s^-1) and quantitative. The product of the reaction, which possesses a ligand-radical coordinated to a Ru(II) center, can be written generically as Ru(bpz)⁺₃, and represented as Ru(bpz)₂(^.bpz^-)⁺ in alkaline solution and its conjugate acid [Ru(bpz)₂(^.bpzH)²⁺; pK_a = 7.1] in acidic solution. The reaction of Ru(bpz)²⁺₃ with ^.OH (k = 5.5 × 10⁹ M^-1 s^-1) yields the OH-adduct to the ring system of the ligands; Ru(bpz)₂(^.bpzOH)²⁺ is unstable toward bimolecular decay (k ∼4× 10⁸ M^-1 s^-1). Reaction with H^. (k = 3 × 10⁹ M^-1 s^-1) results in hydrogenation at a ring-carbon; this product is unstable in the time frame of seconds. No reaction is observed between Ru(bpz)²⁺₃ and Cl^-.₂. Ru(bpz)₂(^.bpz^-)⁺ reduces Co(sep)³⁺ (k = 3.3 × 10⁵ M^-1 s^-1) at pH 10, but there is no reaction at pH 4. However, Ru(bpz)₂(^.bpzH)²⁺ establishes an electron-transfer equilibrium (K_eq = 7) with Cr(bpy)³⁺₃ at pH 3.     

A kinetic study of the permanganate—oxalate reaction and kinetic determination of manganese(II) and oxalic acid by the stopped-flow technique

The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —$\text{d[MnO}{}_4{}^{\mathrm{-}}\text{]}\text{d}\text{t}$ = k [Mn²⁺] [C₂O₄^2-]² [MnO₄^-] [H⁺]^-2 = k' [MnC₂O₄] [MnO₄^-]. The values of k and k' were shown to be 5.4 × 10⁴ M^-1 s^-1 and 8.2 × 10⁴ M^-1 s^-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10^-4 M and 1–10 × 10^-3 M and oxalic acid in the range 0–20 μg ml^-1 can be determined very rapidly with a precision of 1–2%.     

The effect of the double layer on the rate of the Fe3+/Fe2+ reaction on a platinum electrode and the contemporary electron transfer theory

The kinetics of the Fe³⁺/Fe²⁺ reaction on a Pt rotating disc electrode was studied in solutions of 0.5 M H₂SO₄ and 0.5 M Na₂SO₄ (pH 2.2). Taking into account formation of sulphate complexes the conclusion was made that the main contribution to the reaction rate is due to FeSO₄⁺ and FeSO₄ complexes. Extended Tafel plots obtained by Randles analysis from experimental current-voltage curves were corrected for the ₂ potential. The latter was evaluated according to the Gouy-Chapman theory by using the surface charge density values deduced from thermodynamic theory and measurements of other authors. Tafel plots were approximated by parabolas and the reorganization energy was calculated as 33 kJ mol^?1 and 51 kJ mol^?1 for Fe³⁺/Fe²⁺ in H₂SO₄ and Na₂SO₄, respectively. The comparison of these values with theoretically predicted ones was made. From the magnitude of the pre-exponential factor of the true rate constant it was concluded that the Fe³⁺/Fe²⁺ electron transfer reaction is non-adiabatic in nature.     

The investigation of the adsorptive behaviour of electroactive species by means of admittance analysis: Part II. Anion-induced adsorption of cadmium(II) from bromide and iodide solutions at the dropping mercury electrode

The adsorption of Cd(II) has been studied by measuring the interfacial admittance spectra at different dc potentials of the dropping mercury electrode (DME) in solutions of: (a) 1 M KBr+0.48 mM Cd(NO₃)₂,(b) 1 M KI+0.105 mM CdI₂ and (c) 0.1 M NaI+0.9 M NaClO₄ +0.116 mM CdI₂ The experimental data were analysed using the procedures described in Part I of this series. The frequency dependence of the admittance corresponds to that of a reversible electrode reaction with reactant adsorption. The potential dependence of the resulting adsorption parameters can be mathematically described by a Langmuir isotherm for adsorption of Cd(II) with the adsorption energy being at least a quadratic function of potential. Detailed checks on the consistency of this model have been applied and were found to be satisfactory.     

Free radical inactivation of trypsin

Reactivities of free radical oxidants, ^.OH, Br^-·₂ and Cl₃COO^. and a reductant, CO^-·₂, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, ^.OH, Br^-·₂ and CO^-·₂, react with trypsin at diffusion controlled rates, k(^.OH + trypsin) = 8.2 × 10¹⁰ M^-1 s^-1, k(Br^-·₂ + trypsin) = 2.55 × 10⁹ M^-1 s^-1 and k(CO^-·₂ + trypsin) = 2.6 × 10⁹ M^-1 s^-1. Moderately reactive trichloroperoxy radical, k(Cl₃COO^. + trypsin) = 3 × 10⁸ M^-1 s^-1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by ^.OH, Br^-·₂ and CO^-·₂ are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl₃COO^. inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.     

Free Ḃr atom and free radical reactions in the radiolysis of 1,2-dibromoethane (DBE) and other bromohydrocarbons in air-free aqueous solutions

G(Br^-)-values have been evaluated in Ar- and N₂O-saturated 1,2-dibromoethane (DBE), bromobutane, propylbromide and bromopentane (BP) under a variety of experimental conditions in aqueous solutions. G(Br^-) increases with increasing halogenated hydrocarbon concentration and with increasing pH. Free Ḃr atoms formed as a result of e^-_aq and ȮH radical reactions with bromohydrocarbons are considered to initiate a chain reaction. Another chain reaction has been invoked to explain the high G(Br^-) at high pH. Ḃr radicals may form a reactive intermediate with OH^- (BrOH^⨪), which decays to Br^- and ȮH. The ȮH radicals have been found to interact with bromohydrocarbons and eventually yields Br^- ions. The formation of Br^- ions is accelerated both at acidic and alkaline pH in systems containing t-butanol. Dose rate studies in Ar- and N₂O-saturated 1,2-DBE and BP show an increase in G(Br^-)-values at low dose rate and confirm the occurrence of a chain reaction initiated by Ḃr atoms. From these studies the rate constant for the reaction of Ḃr with 1,2-DBE has been calculated to be ∼ 1 × 10⁶M^-1s^-1.     

First green protocols for the large-scale preparation of γ-diisoeugenol and related dihydro(1H)indenes via formal [3+2] cycloaddition reactions

Trans-isoeugenol and related styrenes (trans-isohomogenol or O-benzylated isoeugenol), important components of the essential oil of various tropical plants, dimerize easily in the presence of catalytic amounts of BF₃·OEt₂ in poly(ethylene glycol) with M_n = 400 (PEG-400) or SiO₂-OSO₃H in MeCN via formal [3+2] cycloaddition reaction to give respective natural products (diisoeugenol and its O-substituted analog) with the 1,2-trans-2,3-trans-configuration in excellent yields. γ-Diisoeugenol scale-up preparation has also been described.     

Dealkylation of alkylcobalt complexes by the mercury(II) electrophile

The dealkylation of a variety of RCo(BDMBg)⁺ complexes by Hg²⁺ is discussed. (The ligand BDMBg^- is formed by the condensation of two moles of 2,3-butanedionemonoxime with one mole of 1,3-propanediamine or 1,2-ethanediamine.) The products of the dealkylation reaction are Co^III(BDMBg)(H₂O)²⁺₂ and RHg⁺. All reactions are first order in the [Hg²⁺]. The second order rate constants (k₂) vary from 5.9 M^-1 sec^-1 (R = CH₃) to 5.7 x 10^-3M^-1 sec^-1 (R = n-C₃H₇). The relative rates for R are: CH₃ ? C₂H₅ τ C₆H₅CH₂ τ n-C₄H₉ ? n-C₃H₇. This order and other evidence are indicative of an S_E2 mechanism with an attack by Hg²⁺ on the carbon bonded to the cobalt.     

Metallomesogens derived from benzoxazoles-salicylaldimine conjugates

The synthesis, characterization, and mesomorphic properties of a new series of Schiff bases 2a-h and metal complexes 1a-h-M are prepared and their mesomorphic properties studied. Two single crystallographic structures of 2d (n=12, m=1) and 1g-Pd (n=m=12) were determined by X-ray analysis. Both compounds crystallize in a triclinic space group P−1. A dimeric structure formed by intermolecular H-bonds in 2d was observed, giving nematic phase due to a better aspect ratio. The central geometry at Pd²⁺ ion is nearly perfect square plane. All Schiff bases 2a-h formed N or/and SmC phases. The formation of mesophases of complexes 1a-h-M was strongly dependent on metal ions incorporated. All Cu²⁺, Ni²⁺ and Pd²⁺ complexes exhibited N or/and SmC phase, respectively. However, Zn²⁺ and Co²⁺ complexes were not mesogenic. The lack of mesomorphism was probably attributed to a preferred tetrahedral geometry at Zn²⁺ and Co²⁺ over a square-planar geometry at Cu²⁺ and Pd²⁺.     

Reaction of carboryne with styrene and its derivatives

Reaction of carboryne generated from 1-I-2-Li-1,2-C₂B₁₀H₁₀ with styrene and its derivatives has been studied. In addition to [2+2] cycloaddition reaction and/or ene reaction, an extra-annular [4+2] cycloaddition reaction is also observed, depending upon the substituents on the vinyl unit. The resulting [4+2] cycloaddition intermediates are so reactive that they immediately undergo rearomatization via either a formal 1,3-hydrogen rearrangement or dehydrogenation initiated by hydrogen abstraction with carboryne in biradical form, to give 3,4-dihydronaphtho[1,2]-o-carboranes and naphtho[1,2]-o-carboranes, respectively. In sharp contrast to that of benzyne, further additions of carboryne onto the primary cycloadducts are not observed.     

A pulse radiolysis and flash photolysis study of the radicals SO-2, SO-3, SO-4 and SO-5

Pulse radiolysis and laser-flash photolysis have been used to generate the radicals SO^-₂, SO^-₃, SO^-₄ and SO^-₅. Optical absorption spectra for these radicals and rate constants for their self-reactions have been derived. The decay of SO^-₂, SO^-₃, and SO^-₄ follow simple second-order kinetics; the decay of SO^-₅ is slower and does not follow a second-order rate law when the radical is generated by the pulse radiolysis of an oxygenated sulfite or bisulfite solution, but is second-order when generated by the flash photolysis of an oxygenated dithionate solution. SO^-₂ reacts rapidly with O₂ and a rate constant of 2.4 × 10⁹ M^-1 s^-1 was derived. SO^-₃ also reacts rapidly with O₂ and a rate constant of 1.1 × 10⁹ M^-1 was derived for this reaction. The rate constant for the reaction of H with SO₂ was determined to be 2.9 × 10⁹ M^-1 s^-1.     

Mass spectrometry of charge-transfer complexes of 7,7′,8,8′-tetracyanoquinodimethane-π-donor systems

Electron impact (El) ionization and positive and negative liquid secondary ion mass Spectrometry (pLSIMS and nLSIMS) of eight charge-transfer complexes of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ)-aromatic systems and of the individual π-donors and -acceptors was examined. The El spectra exhibited the molecular ions of both the donor and the acceptor of each complex. The molecular ion of the π-donor was observed in pLSIMS using m-nitrobenzyl alcohol (NBA) if its oxidation potential is lower than 1.2 V, but when the oxidation potential is higher than 1.9 V, no molecular ion was detected. On the other hand, nLSIMS exhibited the molecular ion of TCNQ in all cases. Participation of an excited state of NBA in the ionization process is suggested.     

Helical primary structures of four-membered rings: (M)-trispiro[3.0.0.3.2.2]tridecane

The synthesis of (M)-trispiro[3.0.0.3.2.2]tridecane [(M)-4], the first hydrocarbon with a helical primary structure of four-membered rings, is described. Key step is the kinetic resolution of a cyclobutanone through reduction with bakers' yeast. As compared to its analogue of three-membered rings, (M)-trispiro[2.0.0.2.1.1]nonane [(M)-1], the specific rotation of (M)-4 is cut in three. According to molecular mechanics calculations this could be due to a potential to adopt different conformations, not given in (M)-1, and to the fact, that (M)-4 describes a distinctly shorter section of a helix than (M)-1.     

The formation of cobalt(II) halide complexes containing neutral bidentate ligands

Summary Preparation of cobalt(II) halide complexes with neutral bidentate ligands, including 2-pyridyl alkyl ketones, is reported. 2-Pyridyl alkyl ketones act as monodentate or bidentate ligands depending on the reaction solvent used. Tetrahedral complexes are isolated for all potential -donating neutral ligands.trans-Octahedral complexes are formed only if the neutral ligands are strong -donors and -acceptors. The stereochemistry of cobalt(II) halide complexes is discussed in relation to the nature of the neutral ligands.     

A theoretical study of the protonation of methylindole derivatives

Ab initio calculations on indole and all its mono-substituted methyl derivatives, using an STO-3G minimal basis set, show that the most basic site is C3. Protonation at the nitrogen atom cannot compete with protonation at C3; and C2 is the less basic site in all cases. The basicity increases with methyl substitution, with the only exception of 3-methyl indole. A good linear correlation exists between calculated and corresponding thermodynamics pK values. 2-Aminoindole is a much stronger base than methylindoles and its high pK value can be explained by the strong interactions with the solvent through tautomeric forms which accumulate positive charge at the NH₂ group. Intramolecular quenching of the fluorescence of some indole derivatives involves intramolecular proton transfer to C4 rather than C2. Reasons why ring nitrogens can behave as either π-acceptors or π-donors in this series are discussed.