- and β-cyclodextrin complexes with n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates. A molecular mechanics study of 1:1 and 1:2 associations

Molecular mechanics (MM) methods were employed to evaluate stabilization upon formation of inclusion compounds between two different guest molecules and - and β-cyclodextrins (CDs) for two different stoichiometries 1:1 and 1:2. The two guest molecules studied were n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates with variety of chain lengths. The computed stability for the inclusion compounds between -CDs and n-alkyl carboxylic acids reproduced experimental data reported in the literature. The transition between 1:1/1:2 complexes occurred at an alkyl chain length of n_C=9. It was previously demonstrated by diffusion coefficients measures that a stable 1:2 stoichiometry inclusion compound could be formed between n-alkyl p-hydroxy benzoates and -CD for the chain length n_C>4. The computed results reproduced the experimental ones. The combination between OPLS and GB/SA resulted in better agreements with experiments than those obtained with MM2 and MM3.     

Electronic spectra of the linear magnesium-containing carbon chains MgC2nH (n = 1–5): A CASPT2 study

Complete active space self-consistent-field (CASSCF) approach has been used for the geometry optimization of the X²Σ⁺ and A²Π electronic states for the linear magnesium-containing carbon chains MgC_2nH (n = 1–5). Multireference second-order perturbation theory (CASPT2) has been used to calculate the vertical excitation energies from the ground to selected seven excited states, as well as the potential energy curves of two ²Σ⁺ and two ²Π electronic states. The studies indicate that the vertical excitation energies of the A²Π ← X²Σ⁺ transition for MgC_2nH (n = 1–5) are 2.837, 2.793, 2.767, 2.714, and 2.669 eV, respectively, showing remarkable linear size dependence. Compared with the previous TD-DFT and RCCSD(T) results, our estimates for MgC_2nH (n = 1–3) are in the best agreement with the available observed data of 2.83, 2.78, and 2.74 eV, respectively. In addition, the dissociation energies in MgC_2nH (n = 1–5) are also been evaluated.     

Microcalorimetric titration of a tetra-p-sulphonated calix[4]arene with α,ω-alkyl diammonium ions in an aqueous solution

25,26,27,28-Tetrahydroxycalix[4]arene-5,11,17,23-tetrasulphonate was in a heat-conduction calorimeter titrated with α,ω-alkyl diammonium ions, n=(3–7), in an aqueous solution at pH 7.1. Apparent concentration binding constants (K_c) and enthalpy changes are reported for a 1 : 1 binding model at minimized concentration ranges. The standard Gibbs energy change, ΔG⁰=−RTln K_c, has a non-linear dependence of the alkyl chain length, n. The interaction is strongest at n≥5. A similar trend is observed for the enthalpy change. However, the fit of the experimental data to the 1 : 1 model was quite poor and neither 1 : 2 nor 2 : 1 models gave any further improvement. Concentration-dependent results were also obtained. It is therefore concluded that the interaction observed is more complex.     

Theoretical studies of uracil–(H2O)n (n = 1–7) clusters by ab initio and ABEEMσπ/MM fluctuating charge model

Uracil–(H₂O)_n (n = 1–7) clusters were systemically investigated by ab initio methods and the newly constructed ABEEMσπ/MM fluctuating charge model. Water molecules have been gradually placed in an average plane containing uracil. The geometries of 38 uracil–water complexes were obtained using B3LYP/6-311++G** level optimizations, and the energies were determined at the MP2/6-311++G** level with BSSE corrections. The ABEEMσπ/MM potential model gives reasonable properties of these clusters when comparing with the present ab initio data. For interaction energies, the root mean square deviation is 0.96 kcal/mol, and the linear coefficient reaches 0.997. Furthermore, the ABEEMσπ charges changed when H₂O interacted with the uracil molecule, especially at the sites where the hydrogen bond form. These results show that the ABEEMσπ/MM model is fine giving the overall characteristic hydration properties of uracil–water systems in good agreement with the high-level ab initio calculations.     

Lithiated γ-O-functionalized propyl phenyl sulfides and sulfones of the type Li[CH(SOxPh)CH2CH2OR] (x = 0, 2). [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] – A structurally characterized organolithium inner complex

Lithiation of O-functionalized alkyl phenyl sulfides PhSCH₂CH₂CH₂OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh₃, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH₂CH₂OR}(tmeda)] (α-2a–d) and [Li{o-C₆H₄SCH₂CH₂CH₂OR)(tmeda)] (o-2a–d), respectively, which has been proved by subsequent reaction with n-Bu₃SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu₃SnCH(SPh)CH₂CH₂OR (α-3a–d) and n-Bu₃Sn(o-C₆H₄SCH₂CH₂CH₂OR) (o-3a–d). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3a–c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2a–c and [Li{CH(SPh)CH₂CH₂OR}] (α-4a–b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH₂CH₂Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO₂CH₂CH₂CH₂OR (R = Me, 5a; i-Pr, 5b; CPh₃, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO₂Ph)CH₂CH₂OR] (6a–c) that were found to react with n-Bu₃SnCl yielding the requisite α-stannylated compounds n-Bu₃SnCH(SO₂Ph)CH₂CH₂OR (7a–c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn).     

Simultaneous determination of C1−C8 n-alkyl acetates and corresponding mono-, di- and trichloroacetates on glass capillary columns with programmed temperature rise

Summary Gas chromatography of mixtures of aliphaticn-alkyl acetates (CH₃–COOR), chloroacetates (CHCl₂–COOR), dichloroacetates (CHCl₂–COOR) and trichloroacetates (CCl₃–COOR), where the alcohol chain length (R) varied between 1 and 8, has been studied on SE-30, Carbowax 20M and OV-351 glass capillary columns with programmed temperatures from 50°C at 2, 4, 6, 8 and 10°C/min. Compounds in the homologous series are eluted in the direct order from methyl ton-octyl acetate. The isomeric chloro esters are eluted on SE-30 according to their boiling points in the order: mono-, di- and trichloro isomer, whereas on polar columns di- and trichloro esters are eluted in the reverse order. The complete separation of all 32 individual components from the mixture could not be reached by any single column, the best separation occurred on SE-30. The mixture can, however, be separated by using columns with polar and non-polar stationary phases. The relative retention times for the compounds are given and the retention order discussed.     

Catalytic Performance of Re/Ga2O3/WO3/ZrO2 Catalyst for n-Hexane Isomerization

A series of Re/Ga₂O₃/WO₃/ZrO₂ catalysts were prepared by the impregnation method. The crystalline structure, redox, and acid site distribution of the catalysts were characterized by X-ray powder diffraction, temperature-programmed reduction of H₂, and temperature-programmed desorption of NH₃. Their catalytic performance for n-hexane isomerization was studied. The results showed that the addition of Re greatly affected the redox properties and the acid site distribution of the catalysts. Owing to the presence of Re, n-hexane isomerization was catalyzed by metal and acid sites, and thus the conversion of n-hexane and the selectivity for 2,2-dimethylbutane were significantly increased. Under the conditions of 195 °C, 1.0 MPa, LHSV = 1.0 h⁻¹, and n(H₂)/n(C₆) = 2.0, the conversion of n-hexane over 1.0%Re/1.0%Ga₂O₃/WO₃/ZrO₂ is 84.8%, and the selectivities for 2,2-dimethylbutane, i-hexane, and cracking products (C_5-) are 20%, 97.7%, and 2.1%, respectively. The catalyst is stable during 150 h operation.     

Transport through a slab membrane governed by a concentration-dependent diffusion coefficient: Part IV. D(C)/D0=1+(αC)−β(αC)

Using the specific functional form D(C)/D₀=1+(αC)−β(αC)² an investigation has been made of (isothermal) transport through a slab membrane under ‘simple’ boundary conditions and governed by a diffusion coefficient, D(C), which, with increasing concentration, at first increases, passes through a maximum value and finally decreases. The flux, integral diffusion coefficient and concentration profile characteristic of steady-state permeation have been evaluated; special attention has been paid to the positions of such profiles in relation to the corresponding linear distribution associated with a constant diffusion coefficient.The corresponding transient-state transport has been studied within a framework of the time-lag ‘early-time’ and ‘ ’ procedures. Expressions for the ‘adsorption’ and ‘desorption’ time-lags are given. The concentration-dependence of these time-lags, of the (four) integral diffusion coefficients derived from them and of the arithmetic-mean time-lag ratios have been considered in some detail. The ‘early-time’ and ‘ ’ finite-difference procedures have likewise been employed to derive four further integral diffusion coefficients, so enabling a comparison to be made of the nine integral coefficients pertaining to established experimental techniques.Particular interest attaches to the situation for which n≡β(αC₀)=1 (where C₀ is the ingoing or upstream concentration of diffusant) resulting in D(C₀) being symmetrical about C₀/2. Some consideration has been given, in general, to features of transient-state transport when governed by a symmetrical D(C).     

Theoretical study of electronic spectra of linear carbon clusters HC2nS (n = 1–5)

In this work we report the structures and stabilities of linear carbon clusters HC_2nS (n = 1–5) in their ground states using the B3LYP density functional. The rotational constants at the optimized geometries give excellent agreement with the experimental and previous theoretical values. The vertical excitation energies of the 2²Π ← X²Π transitions at the CASPT2 level are 3.16, 2.66, 2.05, 1.78, and 1.55 eV, respectively, in good agreement with the corresponding observed values of 3.01, 2.48, 2.10, 1.84, and 1.65 eV. Also, the exponential-decay curves for these vertical excitation energies obtained from experiments and theoretical calculations are illuminated.     

Properties of the perovskites, SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3)

The SrMn_1−xFe_xO_3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe³⁺ and Fe⁴⁺. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn⁴⁺, Fe^(4+δ)+ and Fe⁽³⁺⁾⁺. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-e_g orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe⁽³⁺⁾+/Fe^(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution.     

Linear relationships in α,β-unsaturated carbonyl compounds between the half-wave reduction potentials, the frontier orbital energies and the Hammett σp values

A linear relationship between the half-wave reduction potentials of α,β-unsaturated carbonyl compounds R–CHCH–COX and the Hammett σ_p values of R and X is proposed: E_1/2=−1.341σ_p(X)σ_p(R)+1.123σ_p(X)+1.746σ_p(R)−1.694. A linear relationship is also observed for the LUMO's energy values, the absolute chemical hardness η, the chemical potential μ, the electrophilicity power ω, or the polarisation of the ethylenic double bond with the Hammett σ_p values of R and X.     

Powder neutron diffraction of α-UB2C (α-UB2C-type)

The crystal structure of α-UB₂C (low temperature modification below T = 1675(25)°C) was determined from powder X-ray data (RT) and powder neutron diffraction data (at 29 K) employing the Rietveld-Young-Wiles profile analysis method. α-UB₂C crystallizes in the orthorhombic space group Pmma with a = 0.60338(3), B = 0.35177(2), C = 0.41067(2) nm, V = 0.0872 nm³, Z = 2. The residuals of the neutron refinement were R₁ = 0.032 and R_F = 0.043. The crystal structure of α-UB₂C is a new structure type where planar nonregular 6³-U-metal layers alternate with planar nonmetal layers of the type (B₆C₂)³. Boron atoms are in a typical triangular prismatic metal surrounding with a tetrakaidekahedral coordination B[U₆B₂C₁], whereas carbon atoms occupy the center points of rectangular bipyramids C[U₄B₂]. The crystal structure of α-UB₂C derives from the high temperature modification β-UB₂C (ThB₂C-type, ), which reveals a similar stacking of slightly puckered metal layers 6³, alternating with planar layers B₆ · (B₆C₃)². The phase transition from β-UB₂C to α-UB₂C is thus essentially generated by carbon diffusion within the B₆ · (B₆C₃)² layers to form (B₆C₂)³ layers.     

Parity alternation of interstellar molecules cyanopolyynes HCnN (n = 1–17)

In this paper, we report the design of models for interstellar molecules HC_nN (n = 1–17) by means of the B3LYP density functional method. We performed geometry optimization and calculation on vibrational frequency. We find that the ground-state (G-S) isomers of HC_nN (n = 1–17) are with the N atom located at one end and the H atom at the other end of a C_n chain; they are all linear except for HC₂N which is bent. When n is odd, the C_n chain is polyacetylene-like whereas when n is even, the C_n chain displays a structure that is cumulenic-like in the middle of the C_n chain. It is found that the G-S isomers of odd-n HC_nN (n = 1–17) are more stable than those of even-n ones. The finding is in accord with the relative intensities of HC_nN recorded in laboratory investigations, and in consistent with the results of objects observed in interstellar media. We provide explanations for such a trend of even/odd alternation based on concepts of the highest vibrational frequency, bonding character, electronic configuration, incremental binding energy, nucleus-independent chemical shift, and dissociation channels.     

A novel method for the synthesis of (Z)-α-selenyl-α,β-unsaturated ketones via acylation of (E)-α-selanylvinylstannanes

The (E)-α-selenylvinylstannanes react with acyl halides in presence of a catalytic amount of Pd(PPh₃)₄ to give the corresponding (Z)-α-selenyl-α,β-unsaturated ketones in good yield.     

不同硅铝比Cu-ZSM-5纳米片上N2O催化分解

以双季铵盐表面活性剂为模板剂,水热条件下合成了硅铝比(nSi/nAl)为18、26和95的ZSM-5沸石纳米片,采用离子交换方法制备了铜改性的ZSM-5纳米片样品,并测试了其催化分解N_2O性能。结合X射线衍射(XRD)、N_2吸附/脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)、透射电镜(TEM)、氢气程序升温还原(H_2-TPR)、氧气程序升温脱附(O_2-TPD)和原位红外漫反射光谱(CODRIFT)等表征结果 ,探讨了沸石硅铝比对于催化剂N_2O分解性能的影响及其原因。结果表明,ZSM-5纳米片硅铝比越低,CuZSM-5纳米片催化剂的活性越高。催化活性的提高归因于低硅铝比催化剂上Cu~+活性物种可还原性的增强和吸附氧脱附能力的提高。     

Strictly Regiocontrolled α-Monosubstitution of Cyclic Carbonyl Compounds with Alkynyl and Alkyl Groups via Pd-Catalyzed Coupling of Cyclic α-Iodoenones with Organozincs[]

The conditions for the Pd-catalyzed cross coupling of cyclic α-iodoenones, such as 2-iodo-2-cyclohexenone, with alkynylzincs have been optimized. The use of tris(o-furyl)phosphine (TFP) as a ligand and DMF as a solvent has led to the formation of α-alkynylenones in excellent yields. This optimized procedure has been applied to the synthesis of (±)-harveynone and (±)-tricholomenyn A in high yields. Investigation of related α-alkylation reactions using alkylzincs has revealed the following. Methylzinc and primary alkylzinc derivatives readily undergo Pd-catalyzed cross coupling with α-iodoenones. Although (s-Bu)₂Zn also undergoes Pd-catalyzed cross coupling, only the n-Bu-substituted products were obtained. α-Benzylation and α-homobenzylation can proceed satisfactorily, whereas allylzinc and propargylzinc derivatives undergo only addition to the carbonyl group. Although some promising results have been obtained in α-homoallylation and α-homopropargylation, these reactions need to be further improved.     

Reductive Methylation of Homogeneous Primary β-Lauryl/myristyl 7/3 Polyethyleneoxy n = 3–18 Ethylamines under Phase-Transfer Catalysis Conditions

Homogeneous tertiary N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)_nAT, are niche intermediates in the synthesis of homogeneous N-alkyl (C₁–C₁₈)-N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylammonium chlorides (unitary degree of oligomerization of ethylene oxide in the polyoxyethylene chain). This paper synthetically presents the dependence of the reductive methylation yields of homogeneous primary β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)_nAP, on the reaction time (10–90 min), the temperature (70 °C), the molar ratio formic aldehyde /LM(EO)_nAP (1.1/1–2.5/1), the molar ratio HCOOH/LM(EO)_nAP (5/1), the degree of oligomerization of ethylene oxide in the homogeneous polyoxyethylene chain in the 3,6,9,12,18 series, and the structure of the phase-transfer catalysts. The steric effects of hydrophobic groups CH₃ and C₁₈H₃₇ grafted onto the ammonium function, and the micellar phenomena in the vicinity of their critical micellar concentration, directly proportional to the homogeneous degree of oligomerization, were highlighted. In all cases, a steady increase in reductive methylation yields was observed, with even quantitative values obtained. The high purity of the homologous series LM(EO)_nAT will allow their personalization as reference structures for the study of the evolution of basic colloidal characteristics useful in forecasting technological applications. LM(EO)_nAP were obtained either by direct amidoethylation (nucleophilic addition under basic catalysis of homogeneous lauryl/myristyl 7/3 polyethoxylated n = 3, 6, 9, 12, 18 alcohols, LM(EO)_nOH, to acrylamide monomer) or by cyanoethylation of LM(EO)_nOH under basic catalysis at 25–50 °C, in the presence of Fe²⁺ cations as oligomerization/polymerization inhibitor, followed by partial acid hydrolysis of homogeneous β-alkyl (C₁₂H₂₅/C₁₄H₂₉) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionitriles, LM(EO)_nPN, to β-alkyl (C₁₂H₂₅/C₁₄H₂₉) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionamides, LM(EO)_nPD, which led to LM(EO)_nAP by Hoffmann degradation. Homogeneous higher tertiary polyetheramines LM(EO)_nAT were structurally characterized.     

Crystal structure and IR spectrum of 1-O-α- -glucopyranosyl- -mannitol–ethanol (2/1)

1-O-α- -Glucopyranosyl- -mannitol–ethanol (2/1), (C₁₂H₂₄O₁₁)₂–C₂H₅OH, crystallizes in the monoclinic space group P2₁ with unit cell dimensions a=11.4230(8) Å, b=9.525(4) Å, c=15.854(2) Å, β=102.751(7)° and V=1682.4(7) ų, Z=2, D_x=1.45 Mg m⁻³, λ (Mo-K_α)=0.71069 Å, μ=0.128 mm⁻¹, F(000)=788 and T=293(2) K. The structure was solved by direct methods and refined by least-squares calculations on F² to R₁=0.0371[I>2σ(I)], and 0.0930 (all data, 3542 independent reflections, R_int=0.021). There are two molecules of glucopyranosylmannitol (GPM) and one ethanol molecule in the asymmetric unit, and the glucopyranosyl ring adopts a chair conformation in both GPM molecules. Bond lengths and angles accord well with the mean values of related structures. The conformation along the mannitol side chain for one of the GPM molecules was the same as for the known polymorphs of -mannitol, while the conformation of the other molecule was different, indicating different conformational arrangements in the terminal carbon atoms of the mannitol side chains of the two GPM molecules. The structure in 1-O-α- -glucopyranosyl- -mannitol–ethanol (2/1) is held together by a very complex hydrogen bonding system, which consists of an infinte chain propagating along the b-axis and a discontinuous chain, which binds the ethanol molecule to the structure. The FTIR spectra for anhydrous GPM, GPM dihydrate and GPM–ethanol (2/1) were recorded. Both IR and X-ray results indicate the extensive hydrogen bonding in crystalline state.     

η- and η-benzene coordination in [Ag(C6D6)3BF4]

The title complex with one η² and two η¹ deuterobenzene and one monodentate BF₄ ligands was isolated as a by-product in the reaction between [(dppe)RhCl]₂ and EtCl in C₆D₆, in the presence of AgBF₄ and its X-ray crystal structure determined.     

Structures and energies of CnS (1 ≤ n ≤ 20) sulphur carbide clusters

C_nS (1 ≤ n ≤ 20) clusters have been investigated by means of the density functional theory. As a general rule, when 1 ≤ n ≤ 17 the energetically most favorable isomers are found to be the linear arrangement of nuclei (C_∞v) with the sulphur atom at the very end of the carbon chain. The electronic ground state is alternately predicted to be ¹∑⁺ for odd n or ³∑⁻ for even n with a conspicuous odd–even effect in the stability of these clusters. The C₁₈S cluster is predicted to have a S-capped monocyclic structure (¹A₁), but with a low barrier to linearity. On the other hand, C₁₉S and C₂₀S are unambiguously linear in the ¹∑⁺ and ³∑⁻ electronic ground states, respectively.