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91.
The geometrical and energetical parameters of hydrogen fluoride and hydrogen chloride crystals are calculated using the periodic Hartree–Fock method with 6-31G and 6-31G(d,p) basis sets. The comparison of the stabilisation energies reveals that HCl crystals are about 75% less stable than HF crystals. The activation energy for collective proton movements are computed and discussed in view of data of isolated infinite chains. The barriers of 13.1 and 40.0 kcal mol−1 at 6-31G(d,p) level are found for HF and HCl crystals. 相似文献
92.
V. P. Feshin M. Yu. Kon'shin A. V. Radushev E. V. Feshina V. Yu. Gusev A. E. Lesnov V. I. Karmanov 《Russian Chemical Bulletin》1996,45(11):2505-2508
The basicity of hydrazides of the highest aliphatic carboxylic acids RC(O)NHNH2 (R = CnH2n+1,n = 5-12) has been studied by potentiometric titration, and IR and1H NMR spectroscopy.Ab initio Hartree-Fork calculations using the 6–31G* basis set with full optimization of geometry were carried out on the simplest acy1hydrazines and their possible protonated forms. Based on these calculations, and the 1R and1H NMR spectra, the tautomerism of alkylhydrazides and the structures of their protonated forms are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2645–2649, November, 1996. 相似文献
93.
A molecular mechanics software enhanced to perform empirical energy calculations on crystals (KESSHOU) was further developed to handle intermolecular electrostatic interactions as well. The packing of the molecules of 1,4-dicyanobenzene and 1,4-diisocyanobenzene in the crystal was studied. The role of the van der Waals and the electrostatic interactions in the balance of nonbonded atom-atom interactions is analyzed. The packing forces are dominated by van der Waals forces. The electrostatic interactions have higher stabilizing contribution for the dicyano isomer than for the diisocyano form. The dependence of the results on the size of the crystal, the molecular mechanics force field (MM2 vs MM3), and the dielectric constant are also assessed. Ab initio MP2/6–311G** geometries of the isolated molecules are in accordance with the observed benzene ring distortions determined by electron diffraction. 相似文献
94.
Tatiana Murakhtina Jasper Heuft Evert Jan Meijer Daniel Sebastiani 《Chemphyschem》2006,7(12):2578-2584
A combined experimental and ab initio study is presented of the 1H NMR chemical shift distribution of aqueous hydrogen chloride solution as a function of acid concentration, based on Car-Parrinello molecular dynamics simulations and fully periodic NMR chemical-shift calculations. The agreement of computed and experimental spectra is very good. From first-principles calculations, we can show that the individual contributions of Eigen and Zundel ions, regular water molecules, and the chlorine solvation shell to the NMR line are very distinct and almost independent of the acid concentration. From the computed instantaneous NMR distributions, it is further possible to characterize the average variation in hydrogen-bond strength of the different complexes. 相似文献
95.
96.
Inis C. Tornieporth-Oetting Thomas M. Klaptke 《Angewandte Chemie (International ed. in English)》1995,34(5):511-520
The chemistry of covalent inorganic azides originated with the synthesis of aqueous HN3 solutions by Tony Curtis in 1890. A little later, in 1900, it proved possible to prepare iodine azide, IN3, as the first member of the meanwhile complete series of halogen azides. Since then it has been possible to synthesize, in addition to HN3 and the stable salt H2NSbF, azide compounds of elements from Groups 13 to 17. In these compounds the N3 moiety acts as a pseudohalogen and is primarily covalently coordinated to the nonmetal. Only a few organic azides, however, as well as HN3, H2N, and all halogen azides have been thoroughly studied with respect to structure and bonding. The combined application of diffraction methods (X-ray and electron diffraction) and microwave spectroscopy together with quantum chemical approaches such as ab initio SCF and density functional calculations have led in the last few years to an improved understanding of the molecular properties of numerous nonmetal azides, almost all of which are explosive. This interaction of theory and experiment has greatly enhanced the development of azide chemistry and has led to realistic expectations for the synthesis of as yet unknown nonmetal azides. 相似文献
97.
We calculate energy barriers of atom- and proton-transfer reactions in hydrogen-bonded complexes in the gas phase. Our calculations do not involve adjustable parameters and are based on bond-dissociation energies, ionization potentials, electron affinities, bond lengths, and vibration frequencies of the reactive bonds. The calculated barriers are in agreement with experimental data and high-level ab initio calculations. We relate the height of the barrier with the molecular properties of the reactants and complexes. The structure of complexes with strong hydrogen bonds approaches that of the transition state, and substantially reduces the barrier height. We calculate the hydrogen-abstraction rates in H-bonded systems using the transition-state theory with the semiclassical correction for tunneling, and show that they are in excellent agreement with the experimental data. H-bonding leads to an increase in tunneling corrections at room temperature. 相似文献
98.
99.
100.
J. M. Hernndez Ana M. Herrera J. García‐Serrano J. F. Rivas‐Silva 《International journal of quantum chemistry》2002,88(3):342-346
Conformations of p‐methacryloylaminophenylarsonic acid (p‐MAPHA) are determined through molecular mechanics and DFT/B3LYP calculations. Solvation effects are studied within the self‐consistent isodensity continuum model (SCI‐PCM). The stationary points were found to correspond to minima as verified by the analysis of vibrational frequencies in the molecule. The molecular optical absorption was obtained by using different solvent environments. The present results are in good agreement with the available experimental data. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献