Photoelectron Spectroscopy and Structures of X−⋅⋅⋅CH2O (X=F,Cl, Br,I) Complexes

A combined experimental and theoretical approach has been used to investigate X⁻⋅⋅⋅CH₂O (X=F, Cl, Br, I) complexes in the gas phase. Photoelectron spectroscopy, in tandem with time-of-flight mass spectrometry, has been used to determine electron binding energies for the Cl⁻⋅⋅⋅CH₂O, Br⁻⋅⋅⋅CH₂O, and I⁻⋅⋅⋅CH₂O species. Additionally, high-level CCSD(T) calculations found a C_2v minimum for these three anion complexes, with predicted electron detachment energies in excellent agreement with the experimental photoelectron spectra. F⁻⋅⋅⋅CH₂O was also studied theoretically, with a C_s hydrogen-bonded complex found to be the global minimum. Calculations extended to neutral X⋅⋅⋅CH₂O complexes, with the results of potential interest to atmospheric CH₂O chemistry.     

Photoionization mass spectrometry studies of deuterated acetaldehydes CH3CDO and CD3CHO

Investigations of the fragmentation processes of acetaldehyde were performed by photoionization mass spectrometry of its deuterium labeled species CH₃CDO and CD₃CHO. Intramolecular exchange of hydrogen atoms (hydrogen scrambling) was observed. Obviously this process is accompanied by predissociation of the parent ion. Results are compared with previous work on acetaldehyde CH₃CHO.     

Determination of force fields for formaldehyde,acetaldehyde and acetone by the CNDO/force method

CNDO/Force calculations have been done for formaldehyde, acetaldehyde and acetone, and the theoretical force fields evaluated. Experimental force fields are obtained from vibrational frequencies using the least-squares refinement method. The initial force fields considered are based on the bending and interaction force constants obtained from the CNDO/Force calculations and the stretching force constants transferred from chemically related molecules. Vibrational frequencies of H₂CO, D₂CO, HDCO, H₂¹³CO and D₂¹³CO for formaldehyde, CH₃CHO, CH₃CDO, CD₃CHO, CD₃CDO and CH₂DCHO for acetaldehyde, and CH₃COCH₃ CD₃COCH₃ and CD₃COCD₃ for acetone are employed in the force field refinements. The final force fields obtained are found to be reasonable with respect to the diagonal and interaction force constants.     

Infrared spectra of B(OMe)3, ClB(OMe)2 and Cl2BOMe species,isolated CH stretching frequencies and bond strengths

Infrared spectra in the gas phase are reported over the range 3100-500 cm⁻¹ for species of B(OMe)₃, ClB(OMe)₂ and Cl₂BOMe, with CH₃, CD₃ and CHD₂ substitution. A detailed analysis of νCH and νCD data in all three species of Cl₂BOMe yields strong evidence for the presence of three kinds of CH bond, two of them weak and one of them strong. The methyl group is then twisted, probably through 10–20°, out of the eclipsed or staggered conformation. The CHD₂ spectra of the di and trimethoxy compounds are less susceptible to analysis, but suggest also the presence of two weak and strong bonds, the former increasing in weakness as the number of methoxy groups increases. This is as expected from the increased competition likely between the lone pair electrons for the empty boron orbital. The spectra of the CD₃ species permit a clear assignment of νBO, δ_sCH₃, δ_sCD₃ and δ_asCD₃ modes. In Cl(COCH₃)₂, ν_sBO lies at 1278 cm⁻¹.     

The [CH2CHOH.+, CH3CHO] solvated enol radical cation

The bimolecular reaction of the CH₂CHOH^.+ enol ion (m/z 44) with acetaldehyde gives a strongly dominant product,m/z 45, formed mainly by proton transfer from the ion to the molecule. The abundance of the product coming from a H^. abstraction reaction from the neutral, albeit more exothermic, is negligible. In order to explain this result, the long lived [CH₂CHOH^.+, CH₃CHO] solvated ion was generated by reaction of the CH₂CHOH^.+ enol ion with (CH₃CHO) _n in the cell of a Fourier transform ion cyclotron resonance mass spectrometer. The structure of this solvated ion was clearly established. Labeling indicates that [CH₂CHOH^.+, CH₃CHO], upon low energy collisions, reacts by H^. abstraction more rapidly than by H⁺ transfer to the neutral moiety. This shows that the entropic factors are determinant when the enol ion reacts directly with acetaldehyde.     

Experimental Quantification of Halogen⋅⋅⋅Arene van der Waals Contacts

Crystallographic and computational studies suggest the occurrence of favourable interactions between polarizable arenes and halogen atoms. However, the systematic experimental quantification of halogen⋅⋅⋅arene interactions in solution has been hindered by the large variance in the steric demands of the halogens. Here we have synthesized molecular balances to quantify halogen⋅⋅⋅arene contacts in 17 solvents and solvent mixtures using ¹H NMR spectroscopy. Calculations indicate that favourable halogen⋅⋅⋅arene interactions arise from London dispersion in the gas phase. In contrast, comparison of our experimental measurements with partitioned SAPT0 energies indicate that dispersion is sufficiently attenuated by the solvent that the halogen⋅⋅⋅arene interaction trend was instead aligned with increasing exchange repulsion as the halogen increased in size (ΔG_X⋅⋅⋅_Ph=0 to +1.5 kJ mol⁻¹). Halogen⋅⋅⋅arene contacts were slightly less disfavoured in solvents with higher solvophobicities and lower polarizabilities, but strikingly, were always less favoured than CH₃⋅⋅⋅arene contacts (ΔG_Me⋅⋅⋅_Ph=0 to −1.4 kJ mol⁻¹).     

Rate constants and Arrhenius parameters for the reactions of Cl atoms with the halogenated ethers: CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2

Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF₃CH₂OCHF₂, CF₃CHClOCHF₂, and CF₃CH₂OCClF₂ using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl₂ in a mixture containing the ether and CD₄. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD₄ → DCl + CD₃. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF₃CH₂OCHF₂: k = (5.1₅ ± 0.7) × 10⁻¹² exp(−1830 ± 410 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CHClOCHF₂: k = (1.6 ± 0.2) × 10⁻¹¹ exp(−2450 ± 250 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CH₂OCClF₂: k = (9.6 ± 0.4) × 10⁻¹² exp(−2390 ± 190 K/T) cm³ molecule⁻¹ s⁻¹ The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001     

Effect of Halide Anions on the Electroreduction of CO2 to C2H4: A Density Functional Theory Study**

The halide anions present in the electrolyte improve the Faradaic efficiencies (FEs) of the multi-hydrocarbon (C₂₊) products for the electrochemical reduction of CO₂ over copper (Cu) catalysts. However, the mechanism behind the increased yield of C₂₊ products with the addition of halide anions remains indistinct. In this study, we analysed the mechanism by investigating the electronic structures and computing the relative free energies of intermediates formed from CO₂ to C₂H₄ on the Cu (100) facet based on density functional theory (DFT) calculations. The results show that formyl *CHO from the hydrogenation reaction of the adsorbed *CO acts as the key intermediate, and the C−C coupling reaction occurs preferentially between *CHO and *CO with the formation of a *CHO-CO intermediate. We then propose a free-energy pathway of C₂H₄ formation. We find that the presence of halide anions significantly decreases the free energy of the *CHOCH intermediate, and enhances desorption of C₂H₄ in the order of I⁻>Cl⁻>Br⁻>F⁻. Lastly, the obtained results are rationalized through Bader charge analysis.     

FTIR and quantum chemical study of LiBr solvation in acetonitrile solutions

FTIR spectroscopy and quantum chemical calculations at the RTF + MP2/6-311G** level of theory with solvation model density (SMD) corrections were used to study ion solvation and association in LiBr/acetonitrile solutions. The aim of this study was to establish the composition and geometry of the predominant ionic species solvated by acetonitrile molecules and to analyse their spectroscopic signatures. The results obtained make it possible to propose an equilibrium between Li⁺Br⁻(CH₃CN)₃, Li⁺(CH₃CN)₄, and anionic Br⁻(CH₃CN)_n complexes with an undetermined n value and bent coordination of the solvent molecules. The calculated wavenumbers and the geometric parameters of the solvated ionic species were found to be in excellent agreement with the experimental data.     

A kinetic investigation of reaction of [Os(N)(CH2SiMe3)4][NBun4] with methyl iodide

A high oxidation state alkylnitridoosmium complex, [Os(N)(CH₂SiMe₃)₄][NBuⁿ₄] acts as a nucleophile in reactions with alkyl halides. Alkylimido complexes, Os(NR)(CH₂SiMe₃)₄, are produced. The reaction between [Os(N)(CH₂SiMe₃)₄]⁻ [NBuⁿ₄] and MeI is second order with k₂= 9.5 x 10⁻⁵ sec^t̄1 M⁻¹ at 23°C in CD₂Cl₂ under pseudo first order conditions. The entropy of activation, ΔS^≠, was found to be −10.6 ± 0.5 cal M⁻¹ K⁻¹ and the enthalpy of activation, ΔH^≠, was found to be 19.6 ± 0.2 kcal M⁻¹. The reaction proceeds faster in polar, non-coordinating solvents than in either non-polar solvents or in solvents which can coordinate to the osmium center.     

Reactions of methyl radicals with acetaldehyde and acetaldehyde-d1. II. BEBO calculations of the temperature dependence of the rate constants

The BEBO method was used to calculate the kinetic isotope effect for formyl-hydrogen abstraction from acetaldehyde by methyl radicals. The calculated isotope effect and experimental ratios of the rate constants obtained at 785°K for the reactions of CH₃ with CH₃CHO and CH₃CDO, together with the theoretical temperature dependence of the specific rates (as formulated by the BEBO theory), were used to obtain rate constants for the steps CH₃ + CH₃CHO → CH₄ + CH₃CO (2a), CH₃ + CH₃CHO → CH₄ + CH₂CHO (2b), and CH₃ + CH₃CDO → CH₃D + CH₃CO (1a) between 298 and 1224°K. It was shown that the curvature apparent in the Arrhenius plot of the rate coefficient k₂ reported for the reaction of methyl radicals with acetaldehyde in the temperature range of 298–1224°K is caused both by the simultaneous contribution of steps (2a) and (2b) to methane formation, and by the curvature in the Arrhenius plots of the two elementary rate constants themselves. The predicted curve agrees well with the experimental data, especially if the tunneling correction is applied.     

Phosphorescence and energy assignment of acetaldehyde-d4(3A″) in the vapor phase

The phosphorescence spectrum of CD₃CDO(³A″) has been obtained by collisional sensitization with triplet state sensitizers. The energy of CD₃CDO(³A″) has been assigned at 27 400 ± 200 cm^?1.     

Three-body dissociation dynamics of (SO2)3 studied through dissociative photodetachment of (SO2)3−

The dissociative photodetachment dynamics of (SO₂)₃⁻ were studied by photoelectron–photofragment coincidence spectroscopy at 258 nm. Correlation between the photoelectron and photofragment translational energies was observed as previously seen in the dimer system, implying the presence of a dimer core. The three-body dissociation dynamics of (SO₂)₃ after photodetachment are consistent with a dimer core solvated by a spectator SO₂ molecule with a broad distribution in initial geometry.     

Vibration-rotation transition probabilities in CH+ and CD+

Vibrational dipole matrix elements and radiative transition probabilities have been evaluated from electric dipole moment functions for the X¹Σ⁺ states of CH⁺ and CD⁺, which were calculated from highly correlated electronic wavefunctions. The dipole moments in ν = 0 amount to 1.679 D (CH⁺) and 1.313 D (CD⁺), respectively. In comparison to other molecular ions the infrared transition probabilities are found to be rather small. For instance, the Einstein coefficient of spontaneous emission A¹₀ amounts to 1.63 s⁻¹ (CH⁺) and 0.19 s⁻¹ (CD⁺). Dipole moment functions of the neutral CH species in the X²Π and a⁴ Σ⁻ states have also been calculated and are compared with previous theoretical functions.     

Far infrared spectra of methyl nitrate and methyl-d3 nitrate

The far infrared spectra from 300 to 50 cm⁻¹ of methyl nitrate, CH₃ONO₂, and methyl-d₃ nitrate, CD₃NO₂, have been recorded at a resolution of 0.12 cm⁻¹. The fundamental methyl torsional mode has been observed at 204.5 cm⁻¹ (154.2 cm⁻¹ for CD₃ONO₂) with two excited states falling to lower frequencies which gives a V₃ barrier of 980 ± 40 cm⁻¹ (2.80 ± 0.11 kcal/mol). The NO₂ torsion (methoxy) has been observed with the 1 ← 0 transition being at 133.7 cm⁻¹ (119.5 cm⁻¹ for CD₃ONO₂) and eight successive excited states falling to lower frequencies. From these data the twofold barrier to internal rotation has been calculated to be 2650 ± 75 cm⁻¹ (7.69 ± 0.21 kcal/mol).     

Studies of the reactions of thiocyanate ion with chloropentammine Ru(III) dichloride and bromopentammine Ru(III) dibromide and iodopentammine Ru(III) diiodide at various temperatures

New mono-, di- and trinuclear, cationic and anionic species of Ru(III) complexes containing ammonia, thiocyanate and halide ions have been prepared by the reaction of NH₄SCN on[Ru(NH₃)₅X]X₂ (X = Cl⁻, Br⁻, I⁻) at various temperatures. A polynuclear species of RU(II) is also described. The reaction products are temperature dependent. All the compounds have been characterised by chemical analyses, spectral (IR, UV and visible), magnetic susceptibility, polarographic, cyclic voltammetry, conductivity and ion exchange studies. Interconversion among various products has also been described. New acids of Ru(III), H[Ru(NH₃)₂X₃(NCS)] (X = Cl⁻, Br⁻, I⁻) have been isolated and their properties have been studied.     

Study on the method of chemical trapping for formyl intermediates

The method of chemical trapping for formyl intermediates has been studied, with syngas conversion to ethanol over rhodium-based catalysts as the diagnostic reaction concerned, and CH₃I as the trapping reagent. Two species of acetaldehyde, i.e., CH₃CHO and CH₃CDO, were produced in the trapping reaction following CO + 2D₂ reaction. It was shown that the formation of CH₃CHO in the trapping reaction resulted from dehydrogenation of CH₃ from CH₃I to give H, which induced the formation of CH₃CHO in the presence of CO and CH₃ So there may be two pathways for the formation of CH₃CDO in the trapping reaction: one, methylation of DCO adspecies; the other, deuteration of CH₃ CO formed by CO insertion into CH₃ The catalyst surface was purged with Ar following CO + 2D₂ reaction before the trapping reaction was performed. By means of this modified method of chemical trapping for formyl intermediates, CH₃CDO was found to be mainly derived from the methylation of DCO adspecies. Accordingly, it could be concluded that formyl is a C₁ intermediate in the syngas conversion to ethanol over rhodium-based catalysts.     

Triphenyltin hydroxide as a precursor for the synthesis of nanosized tin‐doped TiO2 photocatalysts

¹H and ¹¹⁹Sn NMR results indicate that, when Ph₃SnOH is dissolved in CD₂Cl₂, it dehydrates to (Ph₃Sn)₂O, only a small amount of Ph₃SnOH remaining in equilibrium at room temperature. As a result, the reaction of TiCl₄ with Ph₃SnOH in CH₂Cl₂ proceeds via hydrolysis of the halide to precipitate amorphous TiO₂ that contains adsorbed organotin species. Calcination of the amorphous precursor to 723 K yields nanoparticles of tin‐doped TiO₂ photocatalysts, that contain anatase and rutile phases, and may also contain a segregated SnO₂ phase. The reaction conditions that lead to the formation of a SnO₂ phase have been studied and we have found that it is formed when the amorphous precipitate is not thoroughly washed with CH₂Cl₂ or when non‐recrystallized commercial Ph₃SnOH is used as a starting material. The catalysts obtained have a high activity for the photooxidation of toluene in the gas phase. In particular, a material obtained from non‐recrystallized Ph₃SnOH is particularly promising because the toluene photooxidation rate is more than twice as high as when using Degussa P25. Copyright © 2005 John Wiley & Sons, Ltd.     

Spectra and structure of phosphorus—boron compounds—XXVI. Infrared and Raman spectra,conformational stability and normal coordinate analysis of ethyldichlorophosphine-borane

The Raman (3500-10 cm⁻¹) and infrared (3500-50 cm⁻¹) spectra of solid ethyldichlorophosphine-borane, CH₃CH₂P(BH₃)Cl₂ and its deuterated analog, CH₃CH₂P(BD₃)Cl₂ have been recorded. Additionally, the infrared spectra of the gases and the Raman spectra of the liquids have been recorded and qualitative depolarization ratios have been obtained. Based on the fact that several distinct Raman lines disappear on going from the liquid to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers, with the trans conformer being more stable in the liquid phase, and the only one present in the solid phase. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between the gauche and trans conformers was determined to be nearly zero. Based on Raman depolarization data, group frequencies, isotopic shift factors and infrared band contours, a complete vibrational assignment has been proposed for the trans conformer. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution. The BH₃ torsion has been observed at 188 cm⁻¹, while the BD₃ torsion was not observed. The methyl torsions in the spectra of the solids have been observed at 209 and 202 cm⁻¹ for the “light” and deuterated species, respectively. From the torsional data, barriers to internal rotation have been calculated. The asymmetric torsional mode has been observed for the trans conformer in the infrared spectra of the gas phase at 108 and 104 cm⁻¹ for the BH₃ and BD₃ species, respectively. These results are compared with similar quantities for some corresponding organophosphine—borane compounds.     

Theoretical study of the gas-phase interaction between a chloride ion and a solvent molecule

Ten different ion clusters, ⁻(RH), are investigated by means of SCF and Cl computations in a double-zeta plus polarization basis set. For RH = H₂O, CH₃OH and other compounds with a hydroxy group, Cl⁻ is located along the line somewhat deviated from the extension of the OH bond. This bridge-type structure comes from the electrostatic bonding force plus the minor covalent nature of the OH. Cl⁻ bond. The standard OH...Cl− distance is obtained to be 2.2–2.4 A. The calculated stabilization energies are found to be in reasonable agreement with the available gas-phase experimental values of ΔH⁰ except for Cl⁻(HCOOH).