Calculations of the structural and thermodynamic characteristics of copper carbonates by quantum-chemical methods

The possibility of using the PM5 semiempirical method and the LADY program for calculations of the vibrational properties and thermodynamic characteristics of copper carbonates, malachite and azurite, was considered. The infrared and Raman spectra of these minerals were calculated using the valence force field model of the theory of crystal lattice dynamics with varying force constants. The results closely agreed with the calorimetric and spectroscopic experimental data.     

Determination of hydrogen atom positions in basic lead carbonate hydrocerussite by quantum chemical methods and simulation of the vibrational spectra

Positions of hydrogen atoms in the crystal structure of basic lead carbonate hydrocerussite are determined by the PM5 quantum chemical method. Raman and infrared spectra as well as thermodynamic functions are calculated for this compound by the theory of crystal lattice dynamics.     

Calculations of the enthalpies of formation of oxygen-containing adamantane derivatives by quantum-chemical methods

The enthalpies of formation of oxygen-containing adamantane derivatives were calculated using the semiempirical quantum-chemical PM3, MINDO, AM1, and MNDO methods implemented in the MOPAC package. The calculated and experimental values were compared. The best correlation was obtained for AM1 calculations. This method was therefore used to calculate the enthalpies of formation of 20 oxygen-containing adamantane derivatives.     

Acid-Base Properties of Cefalotin,Cefazoline, and Cefalexin

The acid-base properties of cefalosporines, such as cefalotin, cefazoline, and cefalexin, were studied. The concentration constants of their acid dissociation at 20°C on the background of 0.1, 0.4, 0.7, and 1.0 M solutions of KCl and KNO₃ were determined. Thermodynamic dissociation constants were calculated. The semiempirical PM3 quantum-chemical method was used to calculate the size of the ionic forms of the cefalosporines in the energetically preferred conformations.     

Electrooptical and Conformational Properties of Poly(1-Trimethylsilyl-1-Propynes) with Different Chain Microstructures

The methods of the Kerr effect and solution hydrodynamics were applied to study the electrooptical and hydrodynamic properties of samples of disubstituted polyacetylenes, poly(1-trimethylsilyl-1-propynes), prepared by polymerization of 1-trimethylsilyl-1-propyne with NbCl₅ and TaCl₅/BuLi as catalysts. The experimental electrooptical characteristics of polymers were compared with those calculated by PM3 semiempirical quantum-chemical method.     

A study of electronic structure of SbCl5.L and SnCl4.L2 complexes by the PM3 method

Electronic structures of SbCl₅.L and SnCl₄.L₂ complexes were studied by the semiempirical PM3 method. The results were compared with the data from ³⁵Cl NQR and ¹²¹Sb NQR studies and Mössbauer spectra.

A good correlation was obtained between the calculated and experimental values of quadrupole coupling constants. The calculated energies of the donor-acceptor bond formation were compared with the degree of electron density transfer. The derived correlation dependences between the above two parameters suggest different properties for cis and trans complexes.     

A study of electronic structure of SbCl5.L and SnCl4.L2 complexes by the PM3 method

Electronic structures of SbCl₅.L and SnCl₄.L₂ complexes were studied by the semiempirical PM3 method. The results were compared with the data from ³⁵Cl NQR and ¹²¹Sb NQR studies and Mössbauer spectra.

A good correlation was obtained between the calculated and experimental values of quadrupole coupling constants. The calculated energies of the donor-acceptor bond formation were compared with the degree of electron density transfer. The derived correlation dependences between the above two parameters suggest different properties for cis and trans complexes.     

Evaluation of the reactivity of new activated difluoroaromatic compounds

To evaluate the reactivity of new difluroroaromatic compounds in nucleophilic substitution, the positive charges on carbon atoms of C−F bonds were calculated using the quantum-chemical semiempirical PM3 method. A correlation between the charges calculated and the chemical shifts in the¹⁹F NMR spectra was established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 623–625, April, 1998.     

Optical poling effect and optical absorption of cyan, ethylcarboxyl and tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline: experiment and quantum-chemical simulations

We present here results of experimental studies and quantum-chemical simulations of optical absorption and optical poling effects performed on a new synthesized cyan, ethylcarboxyl and tert-buthyl derivatives of 1H-pyrazolo[3,4-b]quinoline incorporated into polymer matrix or dissolved in organic solutions. The efficiency of second-order optical susceptibility d vs photoinduced power density I(p) clearly saturates to certain magnitude d(eff) at sufficient power densities (I(p) > or = 1.3 GW cm(-2)). Comparing experimental data and results of semiempirical quantum-chemical simulations one can conclude that there exists generally a good correlation between the magnitude of saturated susceptibilities d(eff) and macroscopic hyperpolarizabilities for all compounds except the chromophore 1,3-dimethyl-6-cyano-[PQ] only. The discrepancy for this compound may reflect a specific contribution of surrounding polymer matrix. According to the quantum chemical analysis the methyl-containing cyan and ethylocarcoxyl derivatives reveal four/five strong absorption bands in the spectral range 200-500 nm. A substitution of the methyl groups by the phenyl group causes the substantial changes of the absorption spectra mainly in the spectral range 240-370 nm. Measured and calculated absorption spectra manifest rather good agreement mainly in the part regarding the spectral positions of the first oscillator (absorption threshold). The quantum-chemical PM3 method shows the best agreement with experiment. At the same time a considerable broadening almost of all absorption bands appears as a characteristic feature of all measured spectra. The discrepancies between the calculated and the measured spectra are attributed to electron-vibronic coupling as well as to a specific rotational dynamics of phenyl rings.     

Enthalpies of formation of nitro-, nitroxy-, and nitrosoadamantanes

The enthalpies of formation of nitro-, nitroso-, and nitroxyadamantanes were calculated using semiempirical quantum-chemical PM3, MINDO, AM1, and MNDO methods incorporated into MOPAC software package. The best correlation with the experimental data was obtained with the results of PM3 calculations. Using the corresponding linear regression equation, the enthalpies of formation of 22 adamantane derivatives having nitro-, nitroso-, and nitroxy groups were calculated.     

Electronic and steric effect manifestations in the structure of 9-Azidoacridine

The crystal structure of 9-azidoacridine (9AA) was determined by X-ray structure analysis (the compound crystallizes in the rhombic system). The crystallographically independent fragment of the structure of 9AA was found to contain two molecules. Both molecules were nonplanar, and the azido group was displaced out of the acridine nucleus plane by 34.6° (molecule A) and 28.6° (molecule B). The barriers to azido group rotations about the C-N bond were calculated by the semiempirical PM3 and nonempirical DFT B3LYP quantum-chemical methods. According to the B3LYP/6-31G^* calculations, the structures with the azido group situated in the acridine nucleus plane and perpendicularly to this plane are 0.21 and 1.66 kcal/mol, respectively, higher in energy than the completely optimized structure, in which the dihedral angle between the azido group and acridine nucleus planes is 32°. The PM3 method overestimates the steric strain energy of 9AA and underestimates the energy of azido group conjugation with the acridine nucleus compared with B3LYP calculations.     

Enthalpy of formation of thiophene derivatives

The enthalpy of formation in the gas phase has been calculated for 21 carbonyl compounds of the thiophene series with the aid of the PM3, MINDO, AM1, and MNDO semiempirical quantum-chemical methods. Comparison of them with experimental data showed that the best linear correlation was achieved with the PM3 method. The latter in conjunction with a developed linear regression equation has been used to predict the enthalpy of formation of 22 carboxylic acids and ketones of the thiophene series.     

聚苯基-1,3,5-三嗪的高温水解研究

对聚苯基-1,3,5-三嗪及其模型化合物在250℃/3.97MPa高温水中的水解行为进行了研究。聚苯基-1,3,5-三嗪的红外谱图在水解过程中基本保持不变,表明它是一种耐高温水解性能优良的高分子。高效液相色谱、高效毛细管泳色谱及液质联用分析表明,聚合物及其模型化合物的主要水解产物是由对称三嗪杂环被水解而生成的芳香酸,由些提出了它们的水解历程。通过对水解速控步骤活化能的量子化学计算,从理论上解释了这种高分子优良和耐高温水解特性。     

Quantum-chemical calculation of the electron affinity of atoms and radicals

The electron affinities of atoms and radicals were determined from energy characteristics (enthalpy and dissociation energy of o-substituted phenol) calculated by quantum-chemical methods with the use of the HyperChem 8.0.8 (Hypercube, Inc.) and GAMESS-US (version September 7, 2006) program packages. The largest correlation coefficient of 0.974 of the electron affinity-dissociation energy relationship for o-substituted phenol was obtained by the semiempirical PM3 method.     

IR and NMR Study of the Structure of Dextran Polyaldehyde

The structure of samples of dextran polyaldehyde synthesized at various pH was studied by IR and ¹³C NMR spectroscopy and PM3 semiempirical quantum-chemical method.     

Spectroscopic, semiempirical and X-ray structural study of the 2:1 complex of a cyclic diamide of o-phthalic acid with water molecule

Cyclic diamide of o-phthalic acid with 3,6-dioxa-octyl-1,8-diamine (CPhDA) was synthesised by a new method and its hydrate structure has been studied by X-ray diffraction, FT-IR, NMR and PM5 semiempirical methods. The crystal of this compound is orthorhombic, space group Pbcn, with a = 16.7033(11), b = 8.8823(5), c = 19.6182(12) and Z = 8. The IR spectrum of the crystal is consistent with the results obtained by the X-ray study and provides spectroscopic evidence for the formation of the H-bonded complex with water molecules. The calculated structure of the complex and the structural parameters are comparable with those determined by the X-ray method.     

Calculation of molecular vibrations: Selective scaling factors for semiempirical force constants

The complete force constant matrices of a set of 50 aliphatic and aromatic hydrocarbons are calculated at the density functional theory B3LYP/6–31+G(d, p) and semiempirical PM3 levels of theory. After transformation from Cartesian to nonredundant internal coordinates, the errors in the semiempirical force constants are systematically analyzed. The force constants of the C(SINGLE BOND)C stretching coordinates can be easily corrected by a second-order fit. Thus, only two parameters are needed to reduce the mean error from 21.2 to 1.23%. The errors of other internal coordinates, particulary those including torsional modes, exhibit a larger diversity. The performance of the correction scheme in predicting vibrational spectra is shown for several examples including buckminsterfullerene (C₆₀). © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 2050–2059, 1997     

陆森黑盐阴离子(Fe_4S_3(NO)_7]~-简正坐标分析

本文采用简正坐标分析法对陆森黑盐阴离子进行红外光谱的理论归属。初始力常数值取自陆森红盐。修正后的计算频率与观测频率吻合良好,平均偏差为2.6％。基于与陆森红盐力常数的对比以及与陆森黑盐晶体结构和电子结构研究结果的对比,讨论了所得力常数的合理性与可靠性。文中同时指出网兜骨架中振动模式的非定域性的特点。     

Synthesis and transformations of metallacycles. 27. Quantum-chemical study of the mechanism of styrene catalytic cyclometallation with triethylaluminum in the presence of Cp2ZrCl2

Cyclometallation of olefins with AlEt₃ in the presence of Cp₂ZrCl₂ affording five-membered monosubstituted cyclic organoaluminum compounds, was studied by the semiempirical quantum-chemical PM3 method. The proposed model of catalytic cycloalumination of styrene catalyzed by Cp₂ZrCl₂ is in a good accordance with experimental data obtained by dynamic NMR spectroscopy.     

Researches by the method of low-temperature adiabatic calorimetry and quantum chemical computation of vibrational states

The temperature dependence of heat capacity of a natural zinc silicate, hemimorphite Zn₄Si₂O₇(OH)₂·H₂O, over the temperature range 5–320 K has been investigated by the method of low-temperature adiabatic calorimetry. On the basis of the experimental data on heat capacity over the whole temperature interval, its thermodynamic functions C _p (T), S(T) and H(T) ? H(0) have been calculated. The existence of a phase transition in the area of 90–105 K determined on the basis of vibrational spectra has been confirmed, and changes of entropy ΔS _tr. and enthalpy ΔH _tr. of the phase transition have been calculated. Hemimorphite heat capacity has also been determined by the calculation methods according to the valence force field model in LADY program. The values of force constants of valence bonds and angles have been calculated by semi-empirical method PM5. The calculated IR and Raman spectra concordant with the experimental spectra have been obtained. The heat capacity values calculated according to the found vibrational states satisfactorily agree with those experimentally obtained with an accuracy of ±1.7% in the area of 120–200 K, and not more than ±0.8% for the interval of 200–300 K. This fact testifies that the calculation of thermodynamic characteristics is correct.