Ab Initio Study of the Acetylene–Allene Rearrangement in 2-Propargylpyrrole, 2-Propargylfuran, and 2-Propargylthiophene

Ab initio (MP4/6-31G*//RHF/6-31+G*) calculations have been performed to study the acetylene–allene rearrangement in X–CH₂–CCH propargyl systems, where X = ethenyl, E-1-butadienyl, 2-pyrrolyl, 2-furanyl, and 2-thienyl. The spatial and electronic structures, as well as the relative stability, of the initial and final acetylene structures and the corresponding allenes are examined. Migration of the triple bond from the terminal position into the chain, including the stage of allene structure formation, is shown to be thermodynamically favorable for the whole series of compounds. The propargyl substituents of heterocycles isomerize as readily as open diene systems. The differences in the isomerization energies in the series of allenyl- and 1-propynyl-substituted pyrrole, furan, and thiophene are mainly due to the differences in the nature of long-range interactions between heteroatoms and the tricarbon system.     

Measurement of the rate constants for the reactions of the IO• radical with sulfur-containing compounds H2S, (CH3)2S, and SO2

The reactions of iodine monoxide (IO^•) with sulfur-containing compounds, which are important for the atmospheric chemistry, are studied. An attempt is made to distinguish between the heterogeneous and homogeneous reaction pathways. It is shown that, under the experimental conditions, the reactions proceed on the wall and generate iodine atoms into the gas phase. It is found that, at room temperature, the rate constants for the gas-phase reactions of IO^• with (CH₃)₂S and H₂S are lower than 2.5 × 10⁻¹⁴ and 8.0 × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, respectively; the rate constant for the gas-phase reaction of iodine monoxide with SO₂ ≤ 5.6 × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹.     

Isodimorphism of the salts 2RbCl · MIICl2 · 2H2O (MII = Mn,Fe, Co,Cu)

The three-component systems RbClMnCl₂H₂O, 2RbCl · CoCl₂ · 2H₂O2RbCl · CuCl₂ · 2H₂OH₂O, 2RbCl · CoCl₂ · 2H₂O2RbCl · MnCl₂ · 2H₂OH₂O have been studied at 25°C. In the 2RbCl · CoCl₂ · 2H₂O2RbCl · CuCl₂ · 2H₂OH₂O system, a discontinuous series of mixed crystals is formed and in the 2RbCl · CoCl₂ · 2H₂O2RbCl · MnCl₂ · 2H₂OH₂O system, a continuous series is present.The unit cell parameters of the 2RbCl · CoCl₂ · 2H₂O double salt were determined: a = 5.586(2) Å, b = 6.469(3) Å, c = 6.988(2) Å, α = 65.31(3)°, β = 87.69(3)°, γ = 84.65(4)°, volume 228.4 ų, Z = 1.The results obtained and discussed in conjunction with the crystal structure data suggest that for 2M^ICl · M^IICl₂ · 2H₂O type salts the triclinic structure is stable only when the large rubidium and cesium ions participate in combinations with non-Jahn-Teller metal(II) ions. In the cases of Jahn-Teller metal(II) ions or with potassium or ammonium ions a tetragonal structure is always stable.     

Infrared spectra of Rh atom reaction products with C2H2: the HRhCCH, RhCCH, RhCCH2, and Rh-η2-C2H2 molecules

Laser-ablated Rh atoms react with C(2)H(2) upon co-condensation in excess argon and neon to form the insertion product HRhCCH, the alkyne RhCCH, the vinylidene RhCCH(2), and the metallacycle complex Rh-η(2)-(C(2)H(2)). These species are identified through (13)C(2)H(2), C(2)D(2), and mixed C(2)HD isotopic substitutions and density functional theory isotopic frequency calculations. The HRhCCH molecule is characterized by the CH stretching mode at 3306.2 cm(-1) (Ar) and 3310.9 cm(-1) (Ne), the Rh-H stretching mode at 2090.8 cm(-1) (Ar) and 2111.0 cm(-1) (Ne), and two CCH deformation modes at 584.3 and 573.3 cm(-1) (Ar) and 587.1 and 580.3 cm(-1) (Ne). The absorptions for the vinylidene RhCCH(2) complex are observed at 3150.9 (Ar), 3147.2 (Ne) (CH stretching), 1690.1 (Ar), 1694.3 (Ne) (CC stretching), and 804.9 (Ar), 810.5 cm(-1) (Ne) (CCH deformation). The metallacycle Rh-η(2)-(C(2)H(2)) complex is also identified through CC stretching and CCH deformation modes. The insertion reaction of ground Rh atom to the C-H bond is spontaneous on the basis of the growth of HRhCCH absorptions upon annealing in both solid neon and argon. Here, we show that atomic Rh can convert acetylene to the simple Rh vinylidene complex, analogous to that found for ligand-supported Rh complexes.     

Influence of the Length of the Alanine Spacer on the Acidic–Basic Properties of the Ac–Lys–(Ala) n –Lys–NH2 Peptides (n?=?0, 1, 2, …, 5)

By using the potentiometric titration method, we have determined the pK _a values of the two terminal lysine groups in six alanine-based peptides differing in the length of the alanine chain: Ac?CLys?CLys?CNH₂ (KK), Ac?CLys?CAla?CLys?CNH₂ (KAK), Ac?CLys?CAla?CAla?CLys?CNH₂ (KAK2), Ac?CLys?CAla?CAla?CAla?CLys?CNH₂ (KAK3), Ac?CLys?CAla?CAla?CAla?CAla?CLys?CNH₂ (KAK4), and Ac?CLys?CAla?CAla?CAla?CAla?CAla?CLys?CNH₂ (KAK5) in aqueous solution. For each compound, the model of two stepwise acid?Cbase equilibria was fitted to the potentiometric-titration data. As expected, the pK _a values of the lysine groups increase with increasing length of the alanine spacer, which means that the influence of the electrostatic field between one charged group on the other decreases with increasing length of the alanine spacer. However, for KAK3, the pK _a1 value (8.20) is unusually small and pK _a2 (11.41) is remarkably greater than pK _a1, suggesting that the two groups are close to each other and, in turn, that a chain-reversal conformation is present for this peptide. Starting with KAK3, the differences between pK _a1 and pK _a2 decrease; however, for the longest peptide (KAK5), the values of pK _a1 and pK _a2 still differ by about 1 unit, i.e., by more than the value of log₁₀ (4)?=?0.60 that is a limiting value for the pK _a difference of dicarboxylic acids with increasing methylene-spacer length. Consequently, some interactions between the two charged groups are present and, in turn, a bent shape occurs even for the longest of the peptides studied.     

Bending modes of the water molecules and the MO stretching modes in the series MF2 · 4H2O (M = Fe,Co, Ni,Zn)

The infrared spectra of the series MF₂·4X₂O (M = Fe, Co, Ni, Zn; X = H, D) are reported in the frequency ranges of the bending vibrations of the water molecules (ν₂) at 296 and ∼100 K and the MO lattice vibrations (ν_MO) at 296 K. Four ν_MO vibrations consisting of two doublets are identified using deuterium substitution. The various ν_ZnO vibrations correlate well with the metal-oxygen distances R(ZnO), and this correlation is further used to calculate R(MO)'s of the remainder of the series and to refine R(ZnO). Four ν₂(H₂O, HDO, D₂O) vibrations, consisting of two sharp overlapping bands flanked by two broad shoulders, are identified. The number of ν₂(H₂O) components, the sequence of ν₂ in the series and the correlation with R(MO) suggest that the ν₂ frequencies are mainly determined by R(MO). Using this assignment the two types of ν₂ bands are assigned to the two types of crystallographically distinct water molecules found in the MF₂·4H₂O structure.     

The Isomeric Structures of H_2GeLiF, the Prototype Germylenoid

Thepropertiesandreactionsofgermylene,R,Gef,anditsderivativeshavebeenwellstudiedl.Germylenereactions,however,canbeperformedusingintermediatesofthetype.MR'GeMX(M=alkalimetal,X=halogen),analogoustocarbenoidsandsilylenoids,Re'CMXandRR'SiMX2'3.Recently,Gasparandhiscoworkerhavesuggestedthatgermylenoid,Me,GeLiCI,shouldbeinvolvedinthereactionofdichlorodimethylgermanewithsubstitutedbutadiene',butlittleisknownexperimentallyandtheoreticallyaboutitsenergy,geometryorelectronicstructure.Soitisnece…     

Why are the Elemental Nonmetals (F2, Cl2, Br2, I2, S8, P4) of so Many Hues or of Any Hues and Where is the Chromophore? Insight into Intera-X–X Bonds

A unique approach is used to relate the HOMO-LUMO energy difference to the difference between the ionization potential (IP) and electron affinity (EA) to assist in deducing not only the colors, but also chromophores in elemental nonmetals. Our analysis focuses on compounds with lone pair electrons and σ electrons, namely X₂ (X = F, Cl, Br, I), S₈ and P₄. For the dihalogens, the [IP – EA] energies are found to be: F₂ (12.58 eV), Cl₂ (8.98 eV), Br₂ (7.90 eV), I₂ (6.78 eV). We suggest that the interahalogen X–X bond itself is the chromophore for these dihalogens, in which the light absorbed by the F₂, Cl₂, Br₂, I₂ leads to longer wavelengths in the visible by a π → σ* transition. Trace impurities are a likely case of cyclic S₈ which contains amounts of selenium leading to a yellow color, where the [IP – EA] energy of S₈ is found to be 7.02 eV. Elemental P₄ with an [IP – EA] energy of 9.09 eV contains a tetrahedral and σ aromatic structure. In future work, refinement of the analysis will be required for compounds with π electrons and σ electrons, such as polycyclic aromatic hydrocarbons (PAHs).     

Molecular, Thermodynamic, and Kinetic Parameters of the Free Radical C2H5 · in the Gas Phase

The wave function, energy, equilibrium geometry, and normal vibration frequencies of the ground state of the free radical C₂H₅ ^· were obtained by ab initio calculations with inclusion of electron correlation effects at the UB3LYP/6-311++G^{* *} level. The resulting molecular parameters were used to estimate the thermodynamic functions of an ideal gas of C₂H₅ ^·. From the thermodynamic functions of C₂H₅ ^·, I^·, C₂H₅I, C₂H₄, and HI and the kinetic curves of isothermal pyrolysis of ethyl iodide, the absolute rate constants of elementary reactions of free ethyl radical and the mentioned iodine compounds were estimated. The dissociation energy E _{D , 0}(C₂H₅-I) and the standard formation enthalpy _f H ⁰298 (C₂H₅ ^·) were found.     

Topological Studies on the П…П Interactions between OCS, CO2, N2O and Hydrocarbon

采用MP2/aug-cc-pVDZ方法对氧硫化碳（OCS）、二氧化碳（CO2）、一氧化二氮（N2O）与乙烯（C2H4）、乙炔（C2H2）、2-丁炔（C4H6）之间形成的平行构型复合物中的分子间相互作用进行了理论研究.复合物的相互作用能按照B…C2H4〈B…C2H2〈B…C4H6（B=OCS,CO2,N2O）的顺序依次增大,相互作用距离按照B…C2H4〉B…C2H2〉B…C4H6（B=OCS,CO2,N2O）的顺序依次减小.采用电子密度拓扑分析理论方法,讨论了复合物中π…π作用的成键特性.电子密度拓扑分析表明复合物中形成了弱的分子间相互作用,且以静电作用为主;π电子密度分子图与全电子密度分子图中键径方向是一致的,说明π…π作用在本文所讨论的体系中起着很重要的作用.NBO分析表明净电荷迁移从电子给体C2H4,C2H2,C4H6到电子受体OCS,CO2,N2O,迁移数按照B…C2H4〈B…C2H2〈B…C4H6（B=OCS,CO2,N2O）的顺序依次增大,与相互作用能的顺序一致.     

Varying the Lewis base coordination of the Y2N2 core in the reduced dinitrogen complexes {[(Me3Si)2N]2(L)Y}2(μ-η2:η2-N2) (L = benzonitrile, pyridines, triphenylphosphine oxide, and trimethylamine N-oxide)

The effect of the neutral donor ligand, L, on the Ln(2)N(2) core in the (N═N)(2-) complexes, [A(2)(L)Ln](2)(μ-η(2):η(2)-N(2)) (Ln = Sc, Y, lanthanide; A = monoanion; L = neutral ligand), is unknown since all of the crystallographically characterized examples were obtained with L = tetrahydrofuran (THF). To explore variation in L, displacement reactions between {[(Me(3)Si)(2)N](2)(THF)Y}(2)(μ-η(2):η(2)-N(2)), 1, and benzonitrile, pyridine (py), 4-dimethylaminopyridine (DMAP), triphenylphosphine oxide, and trimethylamine N-oxide were investigated. THF is displaced by all of these ligands to form {[(Me(3)Si)(2)N](2)(L)Y}(2)(μ-η(2):η(2)-N(2)) complexes (L = PhCN, 2; py, 3; DMAP, 4; Ph(3)PO, 5; Me(3)NO, 6) that were fully characterized by analytical, spectroscopic, density functional theory, and X-ray crystallographic methods. The crystal structures of the Y(2)N(2) cores in 2-5 are similar to that in 1 with N-N bond distances between 1.255(3) ? and 1.274(3) ?, but X-ray analysis of the N-N distance in 6 shows it to be shorter: 1.198(3) ?.     

Influence of NaI Additions on the Electrical,Dielectric, and Transport Properties in the GeS2–Ga2S3–NaI Glass System

Russian Journal of Electrochemistry - The vitreous system GeS2–Ga2S3 can incorporate a large amount of alkali salts, for example NaI, and such materials have a potential to be used as solid...     

Synthesis of the Ionic Organotin Compounds by the Reaction of PhnSnCl4-n (n=1, 2, 3) with HSCH2COOH

The study of ionic organotin compounds is of current attention owing to their diversified molecular structures and wide range of applications.[1～3] In this paper, we concluded our works on ionic organotin compounds.     

Novel Synthesis of Optically Active 2‐Ethylhexanoic Acid, 2‐Ethylhexanol,and 2‐Ethylhexylamine via the Asymmetric Favorskii Rearrangement

The asymmetric Favorskii rearrangement of optically active α‐haloketones, which are easily prepared from chiral menthyl‐4‐toluenesulfoxide in several steps using primary or secondary amines, yields their corresponding secondary or tertiary chiral amides. The secondary chiral amides were converted to acids or amines using acylation followed by hydrolysis or reduction. In addition, the tertiary amides were directly reduced to alcohol with Super‐Hydride^®.     

Phase equilibria of the Na,K,Mg,Ca//SO4,Cl-H2O system at 50°C in the crystallization range of glaserite 3K2SO4·Na2SO4

Phase equilibria of the Na,K,Mg,Na,K,Mg,Ca//SO₄,Cl-H₂O system are studied at 50°C via translation in the crystallization range of glaserite (3K₂SO₄ · Na₂SO₄). It is found that glaserite as the equilibrium phase of the investigated system at 50°C participates in the formation of 21 invariant points, 21 monovariant curves, and 34 divariant fields. A fragment of the phase equilibria diagram of the investigated system is constructed in the crystallization range of glaserite.