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1.
R. M. Minyaev 《Russian Chemical Bulletin》1996,45(11):2491-2495
The mechanisms of the proton transfer in associates of two molecules of formic acid with one molecule of hydrazine or hydrogen peroxide were studied usingab initio (SCFj6-31G**) method. The mechanism of cooperative (concerted, one-step) four-proton transfer is realized in the associate with the hydrazine molecule. The proton transfer occurs stepwisevia an intermediate in the associate with a hydrogen peroxide molecule. The calculated activation barriers to the proton transfer in the associates investigated are 34.7 kcal mol–1 and 27.1 kcal mol–1, respectively.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2631–2635, November, 1996. 相似文献
2.
The mechanisms of double proton shift in associates HC(O)OH ... X of formic acid with hydrides (X = SiH4, PH3, PH5, H2S, SH4, CIH, and CIH3) were studied by theab initio method (SCF/3G*). The activation barriers to this reaction in associates with PH3, H2S, SH4, CIH, and CIH3 are equal to 68.3, 10.0, 26.0, 1.0, and 0.4 kcal mol–1, respectively. For X = SiH4 and PHS5 transition states for the double proton shift were not determined, and in all of the other cases studied they are synchronous (concerted or one-step).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 817–822, April, 1996. 相似文献
3.
Double proton shifts in associates of formic acid with CH4, NH3, H2O,CH3F,NH2F,HOF, and HF molecules
The mechanisms of double synchronous proton transfer in associates of formic acid with solvent molecules of the HC(O)OHX (X = CH4, NH3, H2O, or HF) and HC(O)OHFHY (Y = CH3F, NH2F, HOF, F2, or HF) types have been studied by anab initio (SCF/3G) method. The calculated activation barriers of the reactions are 78.52, 17.72, 9.91, and 7.06 kcal mol–1 in the former case and 120.1, 259.4, 228.7, 182.8, and 0.35 kcal mol–1 in the latter case. In the latter case, simultaneously with the double transfer of protons, migration of two fluorine atoms along the chain of the associate occurs.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1690–1700, September, 1995.The present work was carried out with financial support from the Russian Foundation for Basic Research (Project Nos. 93-03-4972 and 93-03-18692) and the International Science Foundation (Grant ISF RNJ 000). 相似文献
4.
R. M. Minyaev 《Russian Chemical Bulletin》1998,47(1):8-16
The gradient pathways of the reaction of nucleophilic addition of ammonia to formaldehyde were calculated for free molecules
and in the NH3...H2CO...HC(O)OH complex by theab initio RHF/6-31G**, MP2(fc)/6-31G**, and MP2(full)/6-311++G** methods. Both reactions proceed concertedly. In the first case, the reaction successively passes through two transitional
states with an energy barrier exceeding 35 kcal mol−1. In the case of the complex with formic acid, the reaction follows a conventional pathway, although its activation barrier
calculated by the RHF/6-31G** and MP2(fc)/6-31G** methods decreases to 12.6 and 3.8 kcal mol−1, respectively.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 13–20, January, 1998. 相似文献
5.
Mechanisms of the proton transfer in dimeric associates of formic acid with nitrous, nitric, orthophosphoric, and sulfuric acids were studied by theab initio (HF/6-31G**) method. The mechanism of the cooperative (concerted or one-step) proton transfer was shown to occur in all cases. The calculated activation barriers of the proton transfer reactions for the associates investigated are equal to 19.9, 14.2, 13.3, and 10.7 kcal mol–1, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2184–2189, September, 1996. 相似文献
6.
The gradient pathways of the reactions of nucleophilic addition of H2O and HF molecules to formaldehyde in the gas phase and in the XH…H2CO…HC(O)OH complex (X=OH, F) were calculated by theab initio RHF/6-31G**, MP2(fc)/6-31G**, and MP2(full)/6-311++G** methods. Both reactions proceed concertedly. The formation of H-bonded bimolecular pre-reaction complexes is the initial
stage of the gas-phase reactions; at the same time, no indications of the formation of stable π-complexes were found on the
potential energy surfaces of systems under study. The calculated energy barriers to the gasphase reactions exceed 40 kcal
mol−1, while those to reactions in the complex XH…H2CO…HC(O)OH (X=OH, F) become more than halved.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2146–2154, November, 1998. 相似文献
7.
《Journal of Chemical Sciences》2005,117(5):549-554
In earlier work, the present authors have shown that hardness profiles are less dependent on the level of calculation than
energy profiles for potential energy surfaces (PESs) having pathological behaviors. At variance with energy profiles, hardness
profiles always show the correct number of stationary points. This characteristic has been used to indicate the existence
of spurious stationary points on the PESs. In the present work, we apply this methodology to the hydrogen fluoride dimer,
a classical difficult case for the density functional theory methods. 相似文献
8.
9.
Anab initio MO method has been used to calculate the potential energy surface for the formation of HF when H reacts with C1F. The various
transition states possibly related to forming HF were optimized. An IRC calculation starting from the collinear F-centered
transition state was performed and energies of a series of points with bending configurations were also calculated to determine
the direct reaction path leading to HF product. Another IRC calculation starting from the H-centered transition state was
run to determine the migratory path to forming HF. By doing so, the Polanyi’s assumption that it would involve the direct
and a migratory mechanisms for the formation of HF when H reacts with CIF has been verified theoretically.
Project supported by the National Natural Science Foundation of China. 相似文献
10.
The neutral, cationic, and anionic structures of both prototropic tautomers oftrans- andcis-urocanic acid [(E)- and (Z)-3-(1H-imidazol-4(5)-yl)propenoic acid, respectively] were studied by using semiempirical andab initio gas-phase calculations. Potential energy surfaces of the structures were calculated by using the semiempirical AM1 method, and the geometries corresponding to global minima on these surfaces were optimized up to the MP2/6-31G* level of theory. The calculated protonation forms of each urocanic acid isomer have a planar molecular structure due to a delocalized -electron system, and all of them prefer thes-trans conformation with respect to the bond between the imidazole and the propenoic acid moieties. Thecis-urocanic acid structures are stabilized by an intramolecular hydrogen bond. The chargedcis-urocanic acid isomers have a lower molecular energy than the correspondingtrans-isomers, whereas the neutral molecules have, after inclusion of thermodynamic corrections, approximately the same energy. The cationic urocanic acid structures have about 2500 kJ mol–1 lower energy than the anionic ones and about 1000 kJ mol–1 lower energy than the neutral ones. The nonzwitterionic forms of the neutral urocanic acid isomers have about 200 kJ mol–1 lower energy than the zwitterionic ones. These energy differences are explained by the proton affinities of the imidazole and the propenoic acid moieties of the urocanic acid structures. 相似文献
11.
Reaction of high-temperature solid-state catalytic isotope exchange (HSCIE) of hydrogen in L-hydroxyproline was studied byab initio quantum-chemical calculations. A one-center synchronous mechanism of isotope exchange between the amino acid and the H3O+ model acidic center was considered. The structures of transition states of the reaction and the activation energies were
determined. Relative reactivity of the C−H bonds in the hydroxyproline molecule under conditions of HSCIE was studied. The
results obtained are in agreement with experimental data on the stereoselectivity and regioselectivity of the HSCIE reaction,viz., the lower the calculated activation energy of isotope exchange, the larger the portion of hydrogen substituted by tritium
in a given position of the amino acid molecule. The enhancement of the reactivity under conditions of solid-state isotope
exchange can be associated with additional interaction between the exchanging H atoms and the electron-donor O and N atoms
of the amino acid molecule in transition state.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1056–1060, June, 1999. 相似文献
12.
Nesterova E. G. Gribanova T. N. Minyaev R. M. Minkin V. I. 《Russian Chemical Bulletin》2001,50(2):195-202
The possibility for a specific type of isomerization (electromorphism) to occur in conjugated bicyclic organic compounds containing Group V elements was studied by the ab initio (RHF/6-31G**, MP2(full)/6-31G**), and DFT (B3LYP/6-31G**) methods. Compounds 2 (X = N, P, As) were found to exist in a monocyclic planar form with intramolecular donor-acceptor N...O coordination (X = N) and as aromatic heterapentalene structures with hypervalent O--X--O bonds (X = P, As). According to calculations, no isomerization of planar heteroaromatic structures into pyramidal ones occurs. The strength of the O--X--O hypervalent bond and the aromaticity of heterapentalene structures 2 with ten -electrons increase on going from X = N to X = P. Correct estimation of these effects requires the inclusion of electron correlation. 相似文献
13.
DFT(B3LYP) and 2 quantum chemical calculations have been performed for 1-substituted silatranes XSi(OCH2CH2)N (X = H, CH3, CH2Cl, F), their radical cations, and first ionization potentials (IP1) of these silatranes. The calculated values of IP1 agree well with the experiment and make it possible to assign the first band to IP1 in the photoelectron spectra. Analysis of spin density distribution and electronic charges in the radical cations suggests that ionization occurs mainly due to the lone electron pair of nitrogen, participating in intramolecular coordination. The N → Si interaction is broken, and the N...Si distance increases to 335–340 pm. 相似文献
14.
N. M. Vitkovskaya V. B. Kobychev A. B. Trofimov B. A. Trofimov 《Russian Chemical Bulletin》1997,46(10):1677-1682
The pathways of migration of the multiple bond in propene and propyne molecules involving the hydroxide ion were investigated
by theab initio (RHF/4-31G) method. Stationary points corresponding to stable complexes between the molecules under study and the hydroxide
ion and between the corresponding carbanions and water were found on the pontential energy surfaces of the proton transfer
reactions. There are no transition states with energies exceeding the energies of the initial reagents or those of the end
products on the reaction coordinate. Therefore, the expenditure of energy to overcome the barriers is completely compensated
by the energy gain due to the formation of intermedite complexes. The direction of multiple bond migration by this mechanism
is almost completely determined by the ratio of the energies of the initial reagents and the end products. Account of the
electron correlation and the extension of the basis set do not lead to radical changes in the results.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1772–1777, October, 1997. 相似文献
15.
在550℃~650℃,24 MPa~30 MPa,反应停留16 s~46 s的条件下,对初始浓度0.05 mol/L~0.70 mol/L的甲酸溶液在超临界水中的降解过程进行实验研究。结果表明,甲酸降解的气体产物为H2、CO2和CO,其中H2、CO2为主要产物。高温有利于甲酸降解和H2生成。温度较高(600℃)时,压力变化对甲酸降解无明显影响。在一定范围内延长反应时间可提高气体产物中H2的体积分数和碳气化率。甲酸初始浓度对甲酸降解机理有重要影响,浓度较低(0.1 mol/L)时,甲酸降解主要包含脱羧反应和脱羰反应两条反应路径,其中脱羧反应为主反应路径;浓度较高时则有许多副反应发生。碱性添加剂不利于甲酸降解生成H2。 相似文献
16.
An accurate three-dimensional potential energy surface for the He-Na<Subscript>2</Subscript> complex
An accurate three-dimensional potential energy surface (PES) for the He-Na2 van der Waals complex was calculated at the coupled cluster singles-and-doubles with noniterative inclusion of connected
triple (CCSD(T)) level of theory. A mixed basis set, aug-cc-pVQZ for the He atom and cc-pCVQZ for the sodium atom, and an
additional (3s3p2d1f) set of midbond functions were used. The computed interaction energies in 819 configurations were fitted
to a 96-parameter analytic potential model by least squares fitting. The PES has two shallow wells corresponding to the T-shaped
structure and the linear configuration, which are located at 12.5a
0 and 14 a
0 with depths of 1.769 and 1.684 cm−1, respectively. The who potential energy surface exhibits weak anisotropy. Based on the fitted PES, state-to-state differential
cross sections were calculated.
Supported by the Natural Science Foundation of Anhui Educational Committee (Grant No. 2006kj072A) and the Natural Science
Foundation of Anhui Province (Grant No. 070416236) 相似文献
17.
Yu. A. Borisov 《Russian Chemical Bulletin》1998,47(4):584-586
Ab initio calculations with full optimization of geometry have been carried out with the 6–31 G* basis set on tetrafluoroethylene (with the unrestricted Hartree-Fock method—UHF and the second-order Moller-Plesset perturbation
theory—MP2) and tetratrifluoromethylethylene (with UHF) molecules in the singlet ground and triplet biradical states. The
symmetry of the tetrafluoroethylene molecule in the triplet biradical state was demonstrated to differ from that of ethylene
(D
2d
) due to the deviation of fluorine atoms from CCFF plane. The MP2 optimized geometries of ethylene and tetrafluoroethylene
were used for higher level calculations (MP3, MP4, CCSD). The energy of the ground state singlet-biradical triplet splitting
decreases in the series: ethylene>tetrafluoroethylene> tetratrifluoromethylethylene. These data on energy splitting explain
the increase in reactivity toward the [2+2]-cycloaddition on going from ethylene to tetrafluoroethylene.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 605–607, April, 1998. 相似文献
18.
N. M. Vitkovskaya V. B. Kobychev E. Yu. Larionova B. A. Trofimov 《Russian Chemical Bulletin》1999,48(1):35-41
The pathways of migration of the multiple bond in propene and propyne molecules involving the hydroxide ion were investigated
by theab initio (RHF/6-31+G* and MP2/6-31+G*) methods. Stationary points corresponding to stable complexes between the molecules under study and the hydroxide ion and
between corresponding carbanions and water molecule were found on the potential energy surfaces of the proton transfer reactions.
In the presence of hydroxide ion, migration of the multiple bond can occur by an “intramolecular” mechanism of the proton
transfer involving the proton of hydroxide ion bound in the complex with propene or propyne molecule. For the propene system,
such a mechanism seems to be quite realistic and more preferable energetically than a traditional two-stage mechanism with
a passage of the proton into the medium. For the system with the triple bond, an equal expenditure of energy is required to
follow any mechanism (without taking into account the effects of solvation and the interaction with a cation), whereas the
formation of the stable [H2C=C=CH·H2O]− complex can prevent further transformations.
For Part 1, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–41, January, 1999. 相似文献
19.
The potential energy profile of an isolated CF2ClCOOH molecule with a CF2Cl group rotating around the C–C bond was determined by the Hartree–Fock method using the 6-31G(d) basis set. Barriers to internal rotation were estimated for this molecule; its geometrical parameters were found for the equilibrium and transition states that are due to the torsion potential with unequal wells. Crystal effect on CF2Cl reorientations in solid chlorodifluoroacetic acid has been evaluated. 相似文献
20.
The structure of conformers and potential curves of the internal rotation (PCR) about the O?O and N?O bonds in peroxynitric acid (PNA) were calculated by the unrestricted Hartree-Fock-Roothaan method. The standard valence-split 6–31G and 6–31G* basis sets were used. The presence of two maxima on every curve has been shown. To refine the values of barriers to the internal rotation in the regions of minima and maxima of PCR, calculations taking into account the electron correlation energy have been carried out at the second- and fourth-order Møller-Plesset level of perturbation theory (MP2 and MP4, respectively). At the MP4/6-61G* level of approximation, the barriers to the rotation about the O?O bond are equal to 8.6 kJ mol?1 and 14.7 kJ mol?1, and both barriers to the rotation about the N?O bond are equal to 33.5 kJ mol?1. The results are compared with those published for PCR in hydrogen peroxide and peroxynitric acid. 相似文献