Spectra and Structure of Silicon-Containing Compounds. XXVIII1 Infrared and Raman Spectra,Vibrational Assignment,and Ab Initio Calculations of Vibrational Spectrum and Structural Parameters of Vinyltrichlorosilane

The infrared spectra (3200-50 cm^–1) of gaseous and solid vinyltrichlorosilane, CH₂=CH-SiCl₃, have been recorded. In addition, the Raman spectrum (3200-10 cm^–1) of the liquid has been recorded and quantitative depolarization values obtained. The infrared spectrum of the sample dissolved in liquid xenon (–80°C) has also been recorded. Using the experimental data and normal coordinate calculations with scaled ab initio force constants, the complete vibrational assignment is proposed. The torsional mode was observed in the infrared spectrum of the gas at 69 cm^–1 and the threefold barrier of internal rotation was calculated to be 500 cm^–1 (5.98 kJ/mol). Ab initio calculations have been carried out at the restricted Hartree–Fock level of the theory as well as with full electron correlation by the perturbation method to second order with different basis sets up to 6-311+G(d,p) to obtain the optimized geometries, harmonic force constants, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies. The ab initio predicted structural parameters are compared with those obtained from a previous electron diffraction study.     

Effects of alkali-metal cations on nitrate-ion N-O bond force constants in ionic melts

Measured frequencies from pure nitrate liquids have been used to calculate the force constants for the nitrate ion and the M⁺-NO₃ ^– systems (M⁺ = Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) by a matrix successive-approximation method based on perturbation theory in dependent coordinates. The valency force constants K_q for the N-O bonds are increased by comparison with free NO ₃ ^– . The N-O bond strengthening is not adequately explained by cation-anion interaction because there is electron-density transfer mainly by the mechanism within the NO ₃ ^– . Correction for the vibrational parameters of the interacting particles confirms the previously demonstrated acid-base mechanism for the cation-anion interaction in liquids containing nitrate.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 230–234, March–April, 1989.     

Far-infrared spectrum,barrier to internal rotation,ro structure,and ab initio calculations for acetylacetylene

The far-infrared spectrum has been recorded from 50 to 360 cm^–1 at a resolution of 0.10 cm^–1 for acetyiacetylene (1-butyne-3-one], CH₃C(O)CCH. The fundamental methyl torsion has been observed at 117.94 cm^–1, from which a periodic barrier to internal rotation has been calculated to be 346 cm^–1 (989 cal mol^–1]. Infrared spectra (3500-50 cm^–1] of the gas and solid and the Raman spectra (3500-100 cm^–1) of the gas, liquid, and solid are reported. Utilizing previously reported rotational constants for three isotopic species,r _o structural parameters have been determined for the heavy-atom skeleton. The fundamental vibrational frequencies, barrier to internal rotation, and structural parameters that have been obtained experimentally are compared to those obtained from ab initio Hartree-Fock calculations employing 3-21G, 6-31G, and DZ basis sets and to the corresponding quantities for some similar molecules.     

C-N stretching force constants in cyano complexes

Summary The study of CN bonding in cyano complexes from vibrational spectra can be carried out using a simplified model, the Cotton-Kraihanzel Force Field, giving results in good accord with those obtained by means of more rigorous and complex entangled calculations. Application of the model is also made to mixed cyano complexes for which rigorous force constants are not known, and a good predictive ability is found, particularly for [Pt(CN)₅X]^2– compounds.     

Consideration of vibrational anharmonicity by scaled corrections to the force constants

A method is proposed for introducing scaled corrections to a harmonic force field to take account of vibrational anharmonicity. All the spectra were satisfactorily described by the introduction of only three scaling coefficients in the case of methane and ethane isotopomers.P. N. Lebedev Institute of Physics, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 77–82, January–February, 1993.     

The effect of the nature of a modifying additive (Pt,Zn, Ga) on the activity of oxide and zeolite catalysts in ethane dehydrogenation and aromatization

The catalytic properties of Pt, Zn, and Ga deposited on supports of various natures (Al₂O₃, SiO₂, NaZSM, and HZSM) in the dehydrogenation and aromatization of ethane were investigated. Pt-containing catalysts are the most active in the conversion of ethane: the selectivity with respect to ethylene is 25–87 % depending on the nature of the support. In the presence of Zn- and Ga-containing catalysts the yield of ethylene is 2–3 times lower than with Pt-catalysts. With HZSM modified by Pt, Zn, or Ga aromatic hydrocarbons (ArH) and methane are the main products of ethane transformation. Ga/HZSM is the most efficient catalyst of the aromatization of ethane under the conditions studied (550 °C, 120 h^–1).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 606–609, April, 1994.     

Theoretical investigation of the structure and vibrational spectrum of the Li2CO2 molecule

The special features of the potential-energy surface (PES) and the paths for the intramolecular rearrangements of the Li₂CO₂ molecule have been investigated by the SCF method in the double-zeta Huzinaga—Dunning basis supplemented by d-type polarization functions in the carbon and oxygen atoms (DZ + P). It has been shown that there are two minima, which correspond to C_s and C₂ structures, on the PES of the molcule. All the remaining structures of the molecule considered either correspond to saddle points or do not represent special points on the PES at all. The force constants, vibrational frequencies, and intensities of the vibrational transitions in the IR spectra have been calculated for both isomers in the DZ basis. The theoretical values of the vibrational frequencies and the isotope shifts are in good agreement with the experimental data obtained with matrix isolation: the mean deviation of the scaled theoretical frequencies for the C_s isomer amounts to 13 cm^–1 or 1.6%. An analysis of the Mulliken populations, as well as a comparison of the geometric parameters and force constants of the isomers of Li₂CO₂ with the corresponding parameters of the Li₂O and CO molecules and of the CO₂ ^2– ion, have shown that the chemical bonds in both isomers may be represented by the scheme (Li⁺)₂CO₂ ^2–. The similarity between the PES's of the Li₂CO₂ and Li₂CO₃ molecules has been demonstrated and explained in the framework of the Gillespie—Nyholm model.Ivanovo Chemical-Engineering Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 30–38, March–April, 1991.     

Theoretical study of the force field and vibrational assignments of acetamide and deuterated analogues

The complete harmonic force constants of acetamide have been evaluated by ab initio calculations at the Hartree-Fock level with the 4–31G(d) basis set. The force field was scaled to compensate for the systematic overestimations of the Hartree-Fock-level force constants by empirical factors using the matrix isolation IR spectra of CH₃CONH₂ and CD₃CONH₂. A normal coordinate treatment has been carried out with the scaled force field to analyze the vibrational spectra of CH₃CONH₂. A normal coordinate treatment has been carried out with the scaled force field to analyze the vibrational spectra of CH₃COND₂, cis-CH₃CONHD and trans-CH₃CONHD. The effect of cis/trans isomerism of CH₃CONHD on the fundamental bands was well reproduced by the calculations. The fundamental vibrations were also predicted for CD₃COND₂, cis-CD₃CONHD and trans-CD₃CONHD.     

Conformational Stability, Raman and Infrared Spectra, Vibrational Assignment, and Ab Initio Calculations of Allyltrifluorosilane

The Raman spectra (3500 to 30 cm^–1) of allyltrifluorosilane, CH₂CHCH₂SiF₃, in the liquid with quantitative depolarization ratios and solid states, and the infrared spectra (3500 to 30 cm^–1) of the gas and solid have been recorded. Additionally, the mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (–100° to –55°C) have been recorded. All of these data indicate there are two conformers, the more stable gauche rotamer and a very small amount of the cis conformer in the fluid states, but only the gauche form remains in the polycrystalline solid. The variable temperature studies of the infrared spectrum of the xenon solution indicate a relatively large enthalpy difference of 354±30 cm^–1 (4.23±0.36 kJ/mol) between the conformers. The fundamental frequencies for the asymmetric (54 cm^–1) and SiF₃ (48 cm^–1) torsions for the gauche conformer were observed in the far infrared spectrum, and from the SiF₃ torsional frequency the barrier to internal rotation is calculated to have a value of 525 cm^–1 (6.28 kJ/mol). A complete vibrational assignment is presented for the gauche conformer that is consistent with the predicted wavenumbers utilizing the force constants from ab initio MP2/6-31G* calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational wavenumbers have been obtained from RHF/6-31G* and/or MP2/6-31G* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with corresponding results for some similar molecules.Taken in part from the dissertation of Y. E. Nashed, which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree     

Vibrational Spectra, Assignment, Conformational Stability and Ab Initio/DFT Calculations for 1-Nitropropane

The infrared spectra (4000–400 cm^{– 1}) of solid and the Raman spectra (3500–30 cm^{– 1}) of liquid and solid 1-nitropropane, CH₃CH₂CH₂NO₂, have been registered. Both the trans and gauche conformers have been identified in the fluid phase, while the trans form remains in the stable solid. Temperature dependence (190–230K) of the liquid 1-nitropropane Raman spectra has been carried out. From these data, the enthalpy difference was determined to be 870 ± 105 J-mol^–1, with the gauche conformer being the more stable rotamer. Ab initio and DFT calculations at different levels of approximation (HF, MP2, B3LYP, B3PW91) gave optimized geometries, harmonic force fields, and vibrational frequencies for the trans and gauche conformers. All the calculations (except the B3PW91/6-31G* level) predicted gauche as the low-energy conformer. Theoretical force constants are analyzed for formulating constraints in the molecular force field model of 1-nitropropane.     

Chemical reaction in chromatographic columns : Dehydrogenation of ethane over cadmium-exchanged zeolite 4A

Pulsed-flow techniques were used to detect considerable differences in the heats of adsorption of ethane and ethylene on various cadmium-exchanged zeolites 4A at temperatures up to 500°C. Higher values (about 10.0 kcal/mole) were observed for ethylene than for ethane (5.0 kcal/mole) at 300–400°C. Experimental verification is provided pertaining to the dehydrogenation of ethane in a gas chromatographic reactor. By appropriate choice of the reaction conditions, conversions up to 80% per pass could easily be obtained at temperatures (400–500°C) at which the thermodynamic equilibrium for a diluted ethane stream (Pc⁺₂ = 0.01-0.1 P_tot.) would not permit more than 25%.     

C2 and C3 hydrocarbon separations in poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes

The transport of olefin and paraffin namely ethane, ethylene, propane and propylene in aromatic poly(1,5-naphthalene-2,2′-bis(3,4-phthalic) hexafluoropropane) diimide (6FDA-1,5-NDA) dense membranes was investigated. The gas permeability coefficients were measured at pressures from 2.5 to 16 atm for the C₂ hydrocarbon gases and pressures up to 8.4 atm for C₃ systems at 35 °C. This membrane exhibits permeabilities of 0.15, 0.87, 0.023 and 0.24 Barrer with respect to pure ethane, ethylene, propane and propylene, and shows an ideal selectivity of 5.8 for the separation of ethylene/ethane, 10 for propylene/propane, 7.6 for nitrogen/ethane and 50 for nitrogen/propane. The olefins showed a preferred permeability to paraffins and discussion were drawn to the permeability, diffusivity and solubility coefficients. The activation energies of permeation, diffusion and solution were also reported and the effect of temperature on the permeation properties was discussed for the pure gas permeability data obtained from 30 to 50 °C. The plasticisation effect was also found for propane and propylene, respectively, although it was neither detected in the saturated nor unsaturated C₂ hydrocarbons at pressures up to 16 atm.     

A new method for the calculation of vibrational force constants. Application to H2

A new method for the quantum mechanical calculation of vibrational force constants is presented. This method is applied to the calculation of the vibrational force constant of H₂, using a completely optimized wavefunction constructed from a single gaussian orbital. The value of the force constant obtained using this method is k₀ = 0.422341088751 au (= 6.5754 × 10⁵ dyne/cm), compared to the value of k₀ = 0.42234079S380 au (= 6.5754 × 10⁵ dyne/cm) obtained using an analytic method, and the experimental value of k_e = 0.3692 au (= 5.748 × 10⁵ dyne/cm).     

Vibrational Spectra and Ion-Pair Properties of Lithium Hexafluorophosphate in Ethylene Carbonate Based Mixed-Solvent Systems for Lithium Batteries

The vibrational spectra of LiPF₆ 1M solutions formed in aprotic mixed solventsobtained by mixing ethylene carbonate with dimethyl carbonate and diethylcarbonate are discussed. The Raman and infrared spectra of lithium hexafluorophosphate(LiPF₆) and the quantum chemical computations of the vibrationalwavenumbers and intensities are reported. Due to the nature of the solutions,attenuated total internal reflectance spectroscopy was used to obtain the infraredspectra. The infrared active vibrational fundamentals of PF₆ ^– provided evidencefor the anion—solvent interaction as well as ion-pair formation. Similarly, theinfrared active modes of the solvent showed significant changes due to thecation—solvent interaction. The computations of the most energetically favorablegeometry in the formation of the Li⁺ PF₆ ion pair are also presented. Conductivitymeasurements carried out for the 1M solutions scanning a wide temperatureinterval (–30 to + 60 °C) confirm the viability of these electrolytes forpractical applications.     

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.     

Vergleichbare Kraftfelder vieratomiger Formylverbindungen

Comparable force fields for HCOO^–, HFCO, HClCO and HDCO have been calculated on the basis of internal coordinates. Linear relations between (i) the carbonyl bond order and the carbonyl stretching force constant, (ii) the sum of the three in-plane bending force constants and the hydrogen out-of-plane force constantf , (iii) a combination of orbital electronegativities andf , have been obtained. The observed in-plane vibrational frequencies have been calculated with an average error of 6.3 cm^–1 or 0.4%.

     

II. Ionic association and mobility in propylene carbonate

Conductance data are reported for Ph₄AsPic, Ph₄PPic, Ph₄SbPic, Hex₄NPic, Bu₄PPic, Et₄NSbCl₆ in propylene carbonate at 25°C in the concentration range 1×10^–4 to 15×10^–4 M. The data were analyzed by the Justice modification of the Fuoss-Hsia equation and all salts studied were found to be associated and to form solvent separated ion pairs. Application of the Barthel-Bjerrum model of ion association permitted calculation of the non coulombic portion of the potentials of mean force, W_±. Ionic limiting equivalent conductances of six ions were calculated using known values of R₄N⁺, and Pic^– ions. Walden products of ions in propylene carbonate were examined in the light of modern ion mobility theories, including Boyd-Zwanzig, Hubbard-Onsager, and Hubbard-Kayser models of ion solvent interactions.     

Determination of the elementary reaction rate constants on the basis of the summary values of the rate constants

Conclusions The rate constants of reactions of atomic oxygen with methane, ethane, ethylene, and propylene along different pathways were determined on the basis of the ratios between the concentrations of the products formed and the summary rate constants measured earlier.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2693–2699, December, 1971.     

Structure and spectra of 1,3,2-dioxaphospholenes. 1. Microwave spectra of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene and its isotopomers in the ground and excited vibrational states

The microwave spectrum of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene (1) was studied in the frequency range from 7 to 53 GHz. Rotational transitions of the parent molecule in the ground and eleven excited vibrational states and those of its mono-substituted ³⁷Cl, ¹³C_Me, and ¹³C_Cycle isotopomers in the ground vibrational state were identified. Rotational constants and partial r _s-structure were obtained. The quartic centrifugal distortion constants, dipole moment components _a = 3.8D and _c = 0.24D (the total dipole moment is 3.81D), and the ³⁵Cl quadrupole coupling constants were determined for the parent molecule. The fine structure of the microwave transitions in the parent molecule was analyzed under the assumption of noninteracting methyl groups. The height of the barrier to internal rotation (V ₃₀ = V ₀₃ = 665 cm^–1) and the frequency of torsional vibrations ( = 167 cm^–1) were found. The frequencies of two lowest vibrational modes corresponding to deformation vibrations of the five-membered ring were estimated (100 cm^–1) from the relative intensities of rotational transitions for different vibrational states.     

Effect of Na+, Li+, Pb2+, Ba2+, Si2+, and Ca2+ cations on force constants of W-O and Mo-O bonds of WO4 2− and MoO4 2− anions in melts

By a matrix method of successive approximations, using perturbation theory, the complete set of force constants has been calculated for the free anions WO,^2– and MoO₄ ^2– and for systems MEO₄ ^2–(M = Na₂ ⁺, Li₂ ⁺, Pb²⁺,Sr²⁺, Ca²⁺; E = W, Mo) on the basis of known frequencies of IR and Raman spectra of the corresponding individual melts. Analysis of the results indicates an increase in the force constants of E-O bond stretching and the bending force constants for AD- and MoO₄ ^2– with increasing specific charge of the cation in a field of singly or doubly charged cations.Deceased.Poltava Engineering Construction Institute. Institute of General and Inorganic Chemistry, Academy of Sciences of the Ukrainian SSSR, Kiev. Translated from Teoreticheskuya i ÉksperimentaI'naya Khimiya, No. 1, pp. 120–123, January–February, 1991. Original article submitted January 12, 1989.