Enthalpies of solvation of ethylene oxide oligomers CH3O(CH2CH2O)nCH3 (n = 1 to 4) in different H-bonding solvents: Methanol,chloroform, and water. Group contribution method as applied to the polar oligomers

The enthalpies of solution and solvation of ethylene oxide oligomers CH₃O(CH₂CH₂O)_nCH₃ (n = 1 to 4) in methanol and chloroform have been determined from calorimetric measurements at T = 298.15 K. The enthalpic coefficients of pairwise solute–solute interaction for methanol solutions have been calculated. The enthalpic characteristics of the oligomers in methanol, chloroform, water and tetrachloromethane have been compared. The hydrogen bonding of the oligomers with chloroform and water molecules is exhibited in the values of solvation enthalpy and coefficient of solute–solute interaction. This effect is not observed for methanol solvent. The thermochemical data evidence an existence of multi-centred hydrogen bonds in associates of polyethers with the solvent molecules. Enthalpies of hydrogen bonding of the oligomers with chloroform and water have been estimated. The additivity scheme has been developed to describe the enthalpies of solvation of ethylene oxide oligomers, unbranched monoethers and n-alkanes in chloroform, methanol, water, and tetrachloromethane. The correction parameters for contribution of repeated polar groups and correction term for methoxy-compounds have been introduced. The obtained group contributions permit to describe the enthalpies of solvation of unbranched monoethers and ethylene oxide oligomers in the solvents with standard deviation up to 0.6 kJ · mol⁻¹. The values of group contributions and corrections are strongly influenced by solvent properties.     

Protolyses of (CH3)3SnM(CH3)3 (M = Sn,Ge, Si,C)

Product and kinetic studies on the reactions of hydrogen chloride in methanol solution with the substrates (CH₃)₃SnM(CH₃)₃ (M = Sn; Ge and Si) show that both SnM and SnCH₃ cleavage reactions occur, at similar rates, and are followed by other reactions giving complex but explicable mixtures of products. Similar behaviour is observed for trifluoroacetolysis in carbon tetrachloride solution, and some intermediates are observable. Trifluoroacetolysis of (CH₃)₃SnC(CH₃)₃ results in exclusive SnCH₃ cleavage. The very slow apparent solvolysis in acetic acid solution is thought to involve reaction with dissolved oxygen.     

DFT studies of structural preference of coordinated ethylene in W(CO)3(PX3)2(CH2CH2) (X=H, CH3, F, Cl, Br, and I)

A set of phosphine complexes of the type W(CO)₃(PX₃)₂(CH₂CH₂) (X=H, CH₃, F, Cl, Br, and I) were investigated by density functional theory method (BP86) to examine the effect of the substituent X on the orientation of C-C vector of the ethylene ligand with respect to one of the metal-ligand bonds as well as the donation and the backdonation in the bonding ligands of phosphine and ethylene. When X=CH₃, H, F, and Cl, the ethylene C-C vector prefers to be coplanar with metal-phosphine bonds, while for the ethylene complexes containing PBr₃ and PI₃ ligands, the structural preference is coplanarity of the ethylene and the metal-carbonyl bonds. The molecular orbital calculations and natural bond orbital analysis were used to examine the structural consequences derived from these complexes. It can be concluded that the structural preferences in the complexes have a clear relation to electronic effects of phosphine ligands. Our calculations for halide phosphine complexes, particularly for PBr₃ and PI₃, allow us to conclude that in addition to electronic effects, steric factors can also affect the orientation of the ethylene ligand in complexes.     

The preparation and properties of some allyltin carboxylates:R3SnOOCR′ (R′ = CH3, CH2Cl), R2Sn(OOCR′)2 (R′ = CH2Cl,CHCl2) and [R2Sn(OOCR′)]2O (R′ = CH2Cl,CHCl2, CCl3)

Triallyl- and diallyltin carboxylates [(CH₂CHCH₂)₃SnOOCR′ with R′ = CH₃ and CH₂Cl, (CH₂CHCH₂)₂Sn(OOCR′)₂ with R′ = CH₂Cl and CHCl₂)] and tetraallyl-1,3-diacyloxydistannoxanes {[(CH₂CHCH₂)₂SnOOCR′]₂ with R′ = CH₂Cl,CHCl₂ and CCl₃}, have been prepared from the reaction of tetraallytin with carboxylic acids in methanol.     

Simulation of dielectric properties and stability of clusters (H2O)i, CO2(H2O)i, and CH4(H2O)i

Molecular dynamics method is used for studying complex permittivity ɛ and the stability of individual water clusters as a function of the number of involved molecules (7 ≤ i ≤ 20) and also the corresponding characteristics of water aggregates with a captured CO₂ or CH₄ molecule. Absorption of the latter molecules leads to considerable changes in dielectric properties and stability of clusters. In particular, upon the addition of a CO₂ molecule to a water cluster, the oscillation parameters of the real and imaginary parts of the permittivity change. Capture of a CH₄ molecule by a water aggregate changes the ɛ(ω) dependence from the relaxation to resonance type. For i ≥ 15, the thermal stability of individual water clusters can be lower than that of aggregates CO₂(H₂O) _i and CH₄(H₂O) _i . The mechanical stability of (H₂O) _{i ≥ 13} clusters can exceed that of heteroclusters under consideration. Clusters (H₂O) _i and CO₂(H₂O) _i have approximately the same dielectric stability, whereas aggregates CH₄(H₂O) _i exhibit lower stability with respect to electric perturbations. Original Russian Text ? A.E. Galashev, V.N. Chukanov, A.N. Novruzov, O.A. Novruzova, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 2, pp. 143–153.     

Thermodynamics of mixing of ethylene oxide oligomers with different end groups in tetrachloromethane: theoretical treatment

In a previous paper we reported the enthalpies of mixing of oligomers of ethylene oxide with different end groups in tetrachloromethane. This paper shows the applicability of the modified theoretical treatment, based on a quasichemical equilibrium of the contacting segmental surfaces originated from Huggins, to our experimental results. The experimental data of ethylene oxide oligomers with methoxy end groups can be described with the energy parameter Δε_αβ, the equilibrium constant K_αβ and the surface ratio r_σ assuming a chemically uniform surface of the oligomer in CCI₄. Ethylene oxides with strong polar OH end groups can be treated successfully with an extended version of the theory with two additional parameters K and ΔΔε for systems containing three different kinds of chemical units.     

Quantum chemical study of ethylene addition to group-7 oxo complexes MO2(CH3)(CH2) (M = Mn, Tc, Re)

Quantum chemical calculations using DFT at the B3LYP level have been carried out for the reaction of ethylene with the group-7 compounds ReO₂(CH₃)(CH₂) (Re1), TcO₂(CH₃)(CH₂) (Tc1) and MnO₂(CH₃)(CH₂) (Mn1). The calculations suggest rather complex scenarios with numerous pathways, where the initial compounds Re1-Mn1 may either engage in cycloaddition reactions or numerous addition reactions with concomitant hydrogen migration. There are also energetically low-lying rearrangements of the starting compounds to isomers which may react with ethylene yielding further products. The [2 + 2]_Re,C cycloaddition reaction of the starting molecule Re1 is kinetically and thermodynamically favored over the [3 + 2]_C,O and [3 + 2]_O,O cycloadditions. However, the reaction which leads to the most stable product takes place with initial rearrangement to the dioxohydridometallacyclopropane isomer Re1a that adds ethylene with concomitant hydrogen migration yielding Re1a-1. The latter reaction has a slightly higher barrier than the [2 + 2]_Re,C cycloaddition reaction. The direct [3 + 2]_C,O cycloaddition becomes more favorable than the [2 + 2]_M,C reaction for the starting compounds Tc1 and Mn1 of the lighter metals technetium and manganese but the calculations predict that other reactions are kinetically and thermodynamically more favorable than the cycloadditions. The reactions with the lowest activation barriers lead after rearrangement to the ethyl substituted dioxometallacyclopropanes Tc1a-1 and Mn1a-1. The manganese compound exhibits an even more complex reaction scenario than the technetium compounds. The thermodynamically most stable final product of ethylene addition to Mn1 is the ethoxy substituted metallacyclopropane Mn1a-2 which has, however, a high activation barrier.     

Molecular structures of [(Ph3Sn)2O3Se] and [(Ph3Sn)2O4Cr](CH3OH)

Molecular structures of [(Ph₃Sn)₂O₃Se] (1) and [(Ph₃Sn)₂O₄Cr](CH₃OH) (2) have been determined using spectroscopic techniques and X-ray analysis. Each structure consists of polymers containing two types of tin centres: one of them is bridged by two oxygen atoms of the trifunctional oxyanion into a helical chain while the other is pendant to this chain. In the case of the chromato derivative the pendant tin is also bonded to the oxygen atom of the solvent (methanol); hydrogen bonds between the methanol and the non-coordinated oxygen of the chromate generate a three-dimensional structure containing tin atoms in a trigonal bipyramidal environment. In contrast, the two tin centres in the non-solvated selenito derivative have distinct geometries (tetrahedral and trigonal bipyramidal). Variable temperature Mössbauer spectroscopy data are consistent with the polymeric structure of the selenito derivative while NMR spectroscopy shows the presence of monomeric species in solution.     

Computational study on the reactions of XO (X = F, Cl and Br) with CH3SO and CH3SO2

Potential energy surface (PES) for the reactions of XO (X = F, Cl and Br) with CH₃SO and CH₃SO₂ have been calculated at MP2/6-311++G(d, p)//B3LYP/6-311++G(d, p) level. It is revealed that all the reactions take place on both singlet and triplet surfaces. The reaction mechanisms of XO (X = F, Cl and Br) with CH₃SO and CH₃SO₂ are similar: the hydrogen abstraction channel of singlet-state PES, which has the overall negative activation energy, should be the dominant channel and CH₂SO (CH₂SO₂) + HOX should be the main products. The reactions of CH₃SO (CH₃SO₂) with XO become thermodynamically favored in the sequence of FO, ClO and BrO. The topological analysis of electronic density shows that a four-member-ring structure appears in the dominant reaction pathway, it turns to three-member-ring structure via a T-shaped structure and the ring structure disappears as the reaction proceeds. Furthermore, the scope of the structure transition region, the appeared position of the four-member-ring structure and the position of T-shaped structure correlated well to the atom which linked to the four-member-ring structure.     

Blue-shifted hydrogen-bonded complexes. II. CH3F(HF)1 n 3 and CH2F2(HF)1 n 3

The equilibrium structures, binding energies, and vibrational spectra of the clusters CH₃F(HF)_{1 n 3} and CH₂F₂(HF)_{1 n 3} have been investigated with the aid of large-scale ab initio calculations performed at the Møller–Plesset second-order level. In all complexes, a strong C–FH–F halogen–hydrogen bond is formed. For the cases n = 2 and n = 3, blue-shifting C–HF–H hydrogen bonds are formed additionally. Blue shifts are, however, encountered for all C–H stretching vibrations of the fluoromethanes in all complexes, whether they take part in a hydrogen bond or not, in particular also for n = 1. For the case n = 3, blue shifts of the ν(C–H) stretching vibrational modes larger than 50 cm⁻¹ are predicted. As with the previously treated case of CHF₃(HF)_{1 n 3} complexes (A. Karpfen, E. S. Kryachko, J. Phys. Chem. A 107 (2003) 9724), the typical blue-shifting properties are to a large degree determined by the presence of a strong C–FH–F halogen–hydrogen bond. Therefore, the term blue-shifted appears more appropriate for this class of complexes. Stretching the C–F bond of a fluoromethane by forming a halogen–hydrogen bond causes a shortening of all C–H bonds. The shortening of the C–H bonds is proportional to the stretching of the C–F bond.     

Effect of solvent on the exchange of ethylene for propylene on cis-PtCl2(C3H6)(TPPTS), TPPTS = P(m-C6H4SO3Na)3

To further understand the effect of water as a solvent in organometallic reactions, the lability of η²-alkenes coordinated to platinum(II) phosphine complexes has been studied in water and chloroform as a comparison of solvent effects on the exchange kinetics and alkene complex stability. ¹H NMR techniques with both deuterated chloroform and a deuterium oxide/deuterated methanol mixture as solvent systems were used at temperatures as low as ?50°C. Reaction of cis-PtCl₂L(η²-C₃H₆) [L?=?PPh₃ (triphenylphosphine) (1a), TPPTS (tris(m-sulfonatophenyl)phosphine) 1b] with ethylene to form cis-PtCl₂L(η²-C₂H₄) (2?a, b) was observed with dependence on the rate by starting platinum complex and ethylene. The role of water on this reaction, as well as its effect on the equilibrium, will be discussed. The equilibrium constant shows preference for coordination of ethylene and the temperature dependence indicates the reaction is entropy controlled.     

Phase transitions in Co(CH3COO)2·4X2O(X = H,D) from temperature-dependent vibrational spectra

The temperature variations of the isolated infrared and Raman modes of CH₃ and H₂O (D₂O) indicate two distinct discontinuities at 270 ± 5 K and 140 ± 5 K. Both stretches and librational modes of CH₃ and H₂O exhibit pronounced changes at both these temperatures and have been attributed to the dynamics of water. Another distinct discontinuity shown by CH₃ modes only at 213 ± 5 is assignable to CH₃ dynamics.     

COPOLYMERIZATION OF ETHYLENE AND PROPYLENE WITH CpCH2CH2CH=CH2)2MCl2(M=Zr,Hf)AND Cp2ZrCl2 CATALYSTS

(CpCH_2CH_2CH = CH_2)_2MCl_2(M=Zr, Hf)/MAO and Cp_2ZrCl_2/MAO (Cp=cyclopentadienyl; MAO=methylaluminoxane) catalyst systems have been compared for ethylene copolymerization to investigate the influence of theligand and transition metal on the polymerization activity and copolymer properties. For both CH_2CH_2CH=CH_2 substitutedcatalysts the catalytic activity decreased with increasing propene concentration in the feed. The activity of the hafnocenecatalyst was 6～8 times lower than that of the analogous zirconocene catalyst, ~(13)C NMR analysis showed that the copolymerobtained using the unsubstituted catalyst Cp_2ZrCl_2 has greater incorporatien of propene than those produced byCH_2CH_2CH=CH_2 substituted Zr and Hf catalysts. The melting point, crystallinity and the viscosity-average molecularweight of the copolymer decreased with an increase of propenc concentration in the feed. Both CH_2CH_2CH= CH_2 substitutedZr and Hf catalysts exhibit little or no difference in the melting point and crystallinity of the produced copolymers. However,there are significant differences between the two zirconocene catalysts. The copolymer produced by Cp_2ZrCl_2 catalyst havemuch lower T_m and X_c than those obtained with the (CpCH_2CH_2CH=CH_2)_2ZrCl_2 catalyst. The density and molecular weightof the copolymer decreased in the order: (CpCH_2CH_2CH=CH_2)_2HfCl_2>(CpCH_2CH_2CH=CH_2)_2ZrCl_2>Cp_2ZrCl_2. The kineticbehavior of copolymerizaton with Hf catalyst was found to be different from that with Zr catalyst.     

Platinumolefin bond strength in Pt(PPh3)2(CH2CH2) and Pt(PPh3)2 {C(CN)2C(CN)2}

The enthalpy of the reaction: Pt(PPh₃)₂ (CH₂CH₂)(cryst.) + C(CN)₂C(CN)₂ (g) → Pt(PPh₃)₂ {C(CN)₂C(CN)₂}(cryst.) + CH₂ CH₂ (g) has been determined as ΔH₂₉₈=?155.8±8.0 kJ·mol^?1, from solution calorimetry. The interpretation, that the platinumethylene bond is much weaker than the platinumtetracyanoethylene bond, is contrary to conclusions drawn recently from electron emission spectroscopic studies, but in agreement with available structural data.     

Trimeric, Cyclic Dimethyltin-Containing Tungstophosphate [{(Sn(CH3)2)(Sn(CH3)2O)( A- PW9O34)}3]21?

The trimeric, cyclic dimethyltin-containing tungstophophate [{(Sn(CH₃)₂)(Sn(CH₃)₂O)(A-PW₉O₃₄)}₃]²¹⁻ (1) has been synthesized in aqueous acidic medium and characterized by IR, elemental analysis, electrochemistry, and FT-ICR MS. Single-crystal X-ray analysis was carried out on Cs₁₂Na₉[{(Sn(CH₃)₂)(Sn(CH₃)₂O)(A-PW₉O₃₄)}₃]·20H₂O (1a), which crystallizes in the trigonal system, space group R3, with a = b = 29.7445(7) ?, c = 15.5915(7) ? and Z = 3. Polyanion 1 is composed of three trilacunary (A-PW₉O₃₄) Keggin fragments that are linked on one side via three isolated dimethyltin groups and on the other side by a (Sn₃(CH₃)₆O₃) unit and three cesium ions, resulting in a cyclic assembly with C _3v symmetry. The discrete molecular, hybrid organic–inorganic 1 was synthesized by reaction of (CH₃)₂SnCl₂ with Na₉[A-PW₉O₃₄] in 0.5 M sodium acetate buffer (pH 4.8). Comparison of several characteristics of the cyclic voltammograms of 1 and (A-PW₉O₃₄)⁹⁻, including the potential location of their reduction peaks, the difference in their current intensities and their qualitative relative electron transfer speeds, supports the conclusion that the solid-state structure of 1 is retained in solution. The presence of (PW₉O₃₄)-based species in solutions of 1 was also confirmed by FT-ICR mass spectrometry. Dedicated to Professor Günter Schmid on the occasion of his 70th birthday.     

A new equation to reproduce the enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from water to aqueous methanol mixtures at 298 K

The enthalpies of transfer of formamide (Form) N-methylformamide (NMF) and N,N-dimethylformamide (DMF) from water to aqueous methanol mixtures are reported and analysed in terms of the new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using the new solvation theory to reproduce the enthalpies of transfer shows excellent agreement between the experimental and calculated data over the entire range of solvent compositions. The analyses show that the solvation of DMF is random in the aqueous methanol mixtures while Form and NMF are preferentially solvated by methanol. It is also found that the interaction of the solutes is stronger with methanol than with water.     

Reactions of free gold cluster cations with H2O, CH3Cl, and mixtures thereof

The reactions of the mass-selected gas-phase gold cluster cations Au₃⁺ and Au₅⁺ with H₂O, CH₃Cl, and mixtures of these reactants were studied under well-defined multi-collision conditions in an octopole ion trap. The reaction of CH₃Cl with the gold cations was found to proceed fast at room temperature, leading to the adsorption of one CH₃Cl molecule at each ‘corner’ atom of the cluster ion. This strong adsorption hindered the coadsorption of other reactants like H₂O. However, a considerable reduction of the CH₃Cl partial pressure led to distinct patterns of H₂O/CH₃Cl coadsorption products. Furthermore, the mass spectra indicated the loss of hydrogen after the reaction of CH₃Cl with Au₃⁺.     

Enthalpies of solution of n-alcohols in formamide and ethylene glycol

The enthalpies of solution of 1-pentanol, 1-hexanol and 1-heptanol and water were determined in formamide and in ethylene glycol, at 25‡C, by macrosolution calorimetry. The observed enthalpies of solution for the n-alcohols are positive in the two solvents, and of similar magnitude. The enthalpy of solution of water is positive in formamide, and negative in ethylene glycol. From the enthalpies of solution, the enthalpies of solvation and the enthalpies of transfer for organic solvent↿ water were calculated. Using our values and literature data for alkanols, it was possible to see that both the enthalpies of solution and the enthalpies of solvation presented a constant CH₂ increment for the entire series, in contrast with their behavior in water. The methylene increments for these properties in different solvents are compared with parameters considered to reflect the cohesive energy of the solvent.     

CH3SH和CH3SLi分子间的锂键和氢键共存型相互作用

在CH₃SLi＋CH₃SH势能面上求得锂键和氢键共存型复合物的两种稳定构型. 频率分析表明, 与单体相比复合物中S(5)—Li(6)键伸缩振动频率发生红移, 而C(8)—H(10)键伸缩振动频率发生蓝移. 经B3LYP/6-311＋＋G**, MP2/6-311＋＋G**及MP2/AUG-CC-PVDZ水平计算的含基组重叠误差(BSSE)校正的复合物?中相互作用能分别为－58.99, －57.87和－62.89 kJ•mol^－1. 采用自然键轨道(NBO)理论, 分析了复合物中单体轨道间的电荷转移, 电子密度重排及其与相关键键长变化的本质等. 采用分子中的原子(AIM)理论分析了复合物中氢键和锂键的电子密度拓扑性质．在极化连续模型(PCM)下, 考察了溶剂化效应. 结果表明, 所考察的水、二甲亚砜、乙醇和乙醚等四种溶剂均使单体间的相互作用能增大, 且溶剂对复合物中的锂键结构及其振动频率具有显著的影响, 而对复合物中的氢键的振动频率影响不大.     

The enthalpies of formation of CH3Mn(CO)5 and of CH3Re(CO)5, and the strengths of the CH3Mn and CH3Re bonds

From measurements of the heats of iodination of CH₃Mn(CO)₅ and CH₃Re(CO)₅ at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔH^o_f[CH₃Mn(CO)₅, c] = ?189.0 ± 2 kcal mol^?1 (?790.8 ± 8 kJ mol^?1), ΔH^o_f[Ch₃Re(CO)₅,c] = ?198.0 ± kcal mol^?1 (?828.4 ± 8 kJ mo^?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn₂(CO)₁₀ and Re₂(CO)₁₀, values are derived for the dissociation energies: D(CH₃Mn(CO)₅) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol^?1 and D(CH₃Re(CO)₅) = 53.2 ± 2.5 kcal mol^?1. In general, irrespective of the value accepted for D(MM) in M₂(CO)₁₀, the present results require that, D(CH₃Mn) = $\text{1}\text{2}$D(MnMn) + 18.5 kcal mol^?1 and D(CH₃Re) = $\text{1}\text{2}$D(ReRe) + 30.8 kcal mol^?1.