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1.
L. S. Khaikin E. A. Zhilinskaya O. E. Grikina L. V. Vilkov 《Russian Chemical Bulletin》1996,45(5):1043-1055
The equilibrium geometric parameters and structures of the transition states of internal rotation for MeP(O)(CN)2, McOP(CN)2, and their isocyano analogs, MeP(O)(NC)2 and MeOP(NC)2, have been calculated by theab initio SCF method and with inclusion of electron correlation effects according to the second-order Muuller-Plesset perturbation theory (MP2). At both levels the 6-31G* basis set has been used. The estimation of relative stability of these tautomeric forms depends largely on the calculation level. The total energies of the cyanides calculated by the MP2 method are 25–30 kcal mol–1 lower than those of the corresponding isocyanides. The oxo-tautomeric forms containing four-coordinate phosphorus are 15–25 kcal mol–1 more stable than the three-coordinate phosphorus aci-derivatives. The internal rotation potential curves of the aci-forms are characterized by a deep minimum for thetrans-arrangement of the methoxy group and phosphorus lone electron pair. Two additional less clearly pronounced minima are located symmetrically on both sides of the weak maximum, which corresponds to thecis-arrangement. The equilibrium oxo-form structures have a staggered configuration of the methyl group with respect to the phosphorus atom bonds.Translated from izvestiyaAkademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1104–1115, May, 1996. 相似文献
2.
Pentacoordination of carbon atom in bicyclic organic compounds of the pentalene type was studied by theab initio RHF/6-31G** and MP2(full)/6-31G** methods. It was shown that intramolecularS
N
2 reactions with energy barriers within the energy scale of NMR spectroscopy can occur in systems in which a linear orientation
of the attacking and leaving groups is realized. The barrier to the intramolecular nucleophilic substitution reaction in 2,3-dihydro-3-formylmethylenefuran
is 36.9 (RHF) and 27.7 kcal mol−1 (MP2) and decreases to 16.4 and 19.4 kcal mol−1, respectively, in the case of diprotonation at the O atoms in this system. For model pentalene type compounds containing
electron-deficient B atoms in the ring, theab initio calculations predict a further decrease in the barrier height (down to less than 10 kcal mol−1).
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1246–1256, July, 1999. 相似文献
3.
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
4.
N. M. Klimenko E. A. Rykova M. L. McKee I. N. Senchenya 《Russian Chemical Bulletin》1999,48(3):417-427
Ab initio MP2/6-31G*//HF/6-31G*+ZPE(HF/6-31G*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements
between low-lying structures of the OBe3F3
+ cation detected in the mass spectra of μ4-Be4O(CF3COO)6 were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six
structures lie in the range 0–8 kcal mol−1 and those of the remaining four structures lie in the range 20–40 kcal mol−1. Two most favorable isomers, aC
2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC
3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers
to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol−1, except for the pyramidalC
3v isomer (∼16 kcal mol−1). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24
kcal mol−1). A planarD
3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe3H3
+ cation, a hydride analog of the OBe3F3
+ ion; the energies of the remaining five isomers are more than 25 kcal mol−1 higher.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 420–430, March, 1999. 相似文献
5.
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
6.
V. G. Avakyan L. E. Gusel’nikov S. L. Gusel’nikov V. F. Sidorkin 《Russian Chemical Bulletin》2005,54(9):2013-2022
The effect of the nature of substituents at sp2-hybridized silicon atom in the R2Si=CH2 (R = SiH3, H, Me, OH, Cl, F) molecules on the structure and energy characteristics of complexes of these molecules with ammonia, trimethylamine,
and tetrahydrofuran was studied by the ab initio (MP4/6-311G(d)//MP2/6-31G(d)+ZPE) method. As the electronegativity, χ, of the substituent R increases, the coordination bond
energies, D(Si← N(O)), increase from 4.7 to 25.9 kcal mol−1 for the complexes of R2Si=CH2 with NH3, from 10.6 to 37.1 kcal mol−1 for the complexes with Me3N, and from 5.0 to 22.2 kcal mol−1 for the complexes with THF. The n-donor ability changes as follows: THF ≤ NH3 < Me3N. The calculated barrier to hindered internal rotation about the silicon—carbon double bond was used as a measure of the
Si=C π-bond energy. As χ increases, the rotational barriers decrease from 18.9 to 5.2 kcal mol−1 for the complexes with NH3 and from 16.9 to 5.7 kcal mol−1 for the complexes with Me3N. The lowering of rotational barriers occurs in parallel to the decrease in D
π(Si=C) we have established earlier for free silenes. On the average, the D
π(Si=C) energy decreases by ∼25 kcal mol−1 for NH3· R2Si=CH2 and Me3N·R2Si=CH2. The D(Si←N) values for the R2Si=CH2· 2Me3N complexes are 11.4 (R = H) and 24.3 kcal mol−1 (R = F). sp2-Hybridized silicon atom can form transannular coordination bonds in 1,1-bis[N-(dimethylamino)acetimidato]silene (6). The open form (I) of molecule 6 is 35.1 and 43.5 kcal mol−1 less stable than the cyclic (II, one transannular Si←N bond) and bicyclic (III, two transannular Si←N bonds) forms of this molecule, respectively. The D(Si←N) energy for structure III was estimated at 21.8 kcal mol−1.
Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1952–1961, September, 2005. 相似文献
7.
Mechanisms of inversion of the bond configuration at the tetrahedral boron center in five-membered chelate cycles of the 1,3,2-oxazaborolidine
and 1,3,2-oxazaborolidene molecules were studied by theab initio MP2(full)/6-31G** method. It was shown that enantiotopomerization occurs by a dissociative mechanism with the cleavage of the B←N bond and
the formation of acyclic intermediates with tricoordinate planar boron atom. The calculated energy barriers to inversion of
tetrahedral bond configurations at boron centers in the two chelate complexes are equal to 13.1 and 15.4 kcal mol−1, respectively. In contrast to 1,3,2-oxazaborolidine, internal rotation about the B−O bond in its unsaturated analog makes
an appreciable contribution to the reaction coordinate.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 250–255 February, 1999. 相似文献
8.
Ab initio HF/6–31G* calculations ofO-vinylacetoxime monohydrates and cations were performed. Each conformer forms two stable H-complexes with participation of
N and O atoms. The former have planar heavy-atom skeletons, whereas the water molecule in the latter is located above the
plane of the proton-acceptor complex. The complexes stabilized by N...HO and O...HO bonds have different dipole moments and
frequencies of the OH stretching vibrations. The most energetically favorable cation is formed by adding a proton to the Cβ atom of the vinyl group ofO-vinylacetoxime. Theap,ap-conformer (ap is antiperiplanar) of this cation is 6.5 and 34.9 kcal mol−1 more stable than the onium cations with the NH+ and OH+ fragments, respectively, and is characterized by polarization and appreciable lengthening of the N−O and C=C bonds.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 597–600, April, 2000. 相似文献
9.
L. S. Khaikin O. E. Grikina V. I. Perevozchikov A. V. Abramenkov V. A. Shlyapochnikov F. R. Cordell J. E. Boggs 《Russian Chemical Bulletin》1998,47(2):213-224
The equilibrium geometry of theN,N-dimethylnitramine molecule and changes in the energy and structural parameters due to the internal rotation of the nitro group and the inversion of the N atom in the amino fragment were calculated by the restricted Hartree-Fock (RHF) method and at the second-order Møller-Plesset (MP2) level of perturbation theory with inclusion of electron correlation using the 6–31 G* and 6–31 G** basis sets. The one-dimensional potential functions of these motions calculated at the RHF/6–31 G* level were approximated by a truncated Fourier and power series, respectively. The frequencies of torsional and inversion transitions were determined by solving direct vibrational problems for a non-rigid model,i.e., taking into account the molecular geometry relaxation. The equilibrium conformation of the molecular skeleton ofN,N-dimethylnitramine is nonplanar. Transition states of the internal rotation of the nitro group and inversion of the amine N atom are characterized by pronounced concerted changes in its bond angles and the length of the N?N bond. In the MP2/6–31 G* approximation, the height of the barrier to internal rotation calculated taking into account the difference in the zero-point vibrational energies is equal to 9.7 kcal mol?1. Inversion in the amino fragment is accompanied by a relatively small energy change at the barrier height of ?1.0 kcal mol?1 calculated in the same approximation. 相似文献
10.
Yu. A. Borisov Yu. A. Zolotarev E. V. Laskatelev N. F. Myasoedov 《Russian Chemical Bulletin》1998,47(8):1442-1445
Ab initio calculations of molecular and electronic structures of neutral molecules and protonated forms of methionine and its derivatives
in the gaseous phase were carried out by the Hartree-Fock method using the 6–31G* basis set with full geometry optimization. Proton affinities of methionine (1), methionine sulfoxide (2), and methionine
sulfone (3) were calculated for different modes of coordination of the proton. The results of calculations demonstrated that
in protonated forms of 1 and 3, bonding between the proton and the N atom is most favorable, while in protonated form of 2,
bonding between the proton and the O atom of the SO group is most favorable. The proton affinities of the amino acids are
as follows: 223.2 (1), 241.2 (2), and 221.5 (3) kcal mol−1,i.e., methionine sulfoxide 2 exhibits the highest proton affinity in the series of the amino acids under consideration.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1487–1490, August, 1998. 相似文献
11.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1994,50(3):609-619
The conformational stability, barriers to internal rotation and vibrational frequencies of trivinylborane have been determined from the vibrational spectra and ab initio calculations. The ab initio calculations have been carried out utilizing the RHF/3-21G, RHF/6-31G*, and MP2/6-31G* basis sets and support the vibrational data that there are two stable conformations in the fluid phases separated by a relatively small energy difference. One of the conformations is a near-planar form which has the three vinyl groups twisted out of the BC3 plane and belongs to the C3 point group. The other conformer has a non-planar structure and belongs to the C1 point group. These and other calculated results are compared to the corresponding quantities obtained from the experiment. 相似文献
12.
E. G. Baskir I. P. Klimenko Yu. V. Tomilov O. M. Nefedov 《Russian Chemical Bulletin》2005,54(5):1100-1104
The electronic structures and dissociation energies of diazocyclopropane (1), diazomethane (2), 2-diazopropane (3), and diazocyclobutane (4) were calculated at the density functional B3LYP and the ab initio MP2 levels using the 6-31G(d) basis set and at the G2(MP2,SVP)//B3LYP/6-31G(d) level. Distinctive features of diazocyclopropane
1 are the low energy of dissociation with loss of the nitrogen molecule; ΔE = 18.7 kcal mol−1, B3LYP; 9.2 kcal mol−1, G2 at 0 K) and a nonplanar structure, in which the C=N bond forms an angle of 115.7° with the plane of the cyclopropane
ring. The behavior of molecules 1 and 2 in the 1,3-dipolar cycloaddition to ethylene (5), acrylonitrile (6), and methyl acrylate (7) was studied. The reactions of 1 with 6 and 7 have very low activation barriers (ΔE
a = 4.7 and 4.4 kcal mol−1, respectively; at the B3LYP level). For these reactions, the G2 method gives even smaller activation parameters (1.8 and
0.3 kcal mol−1, respectively). The results of our calculations provide a good explanation for high reactivity of diazocyclopropane 1.
Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1072–1076, May, 2005. 相似文献
13.
V. G. Avakyan V. B. Nazarov M. V. Alfimov A. A. Bagatur'yants 《Russian Chemical Bulletin》1999,48(10):1833-1844
The structure of β-cyclodextrin (β-CD), as well as the structure and energetics of β-CD-naphthalene, β-CD-fluorene, β-CD-phenanthrene, β-CD-cyclohexane (1:1), and β-CD-naphthalene (2:2) inclusion complexes was studied by the semiempirical MNDO/PM3 method. Calculations of a β-CD-naphthalene-cyclohexane (1:1:1) complex were also performed. The minimum heat of formation was found for the symmetric β-CD conformation withC 7 symmetry axis. The structure is stabilized by the ring of interunit H-bonds formed by the protons of the 2-OH groups and the O atoms of the 3′-OH groups of the glucose units. Preferableness of this orientation of interunit H-bonds was confirmed byab initio calculations of the molecule of α-(1–4)-glucobiose (maltose) in the MP2/6-31G(d,p)//6-31G(d,p) approximation. The formation of any inclusion compounds of β-CD with arenes is energetically favorable: the complexation energy varies in the range −9 to −12 kcal mol−1. Among complexes with naphthalene, that of composition 2:2 is the most energetically favorable, which is in agreement with experimental data. In this complex, β-CD exists as a dimer of the “head-to-head” type, in which both partners are linked by a system of H-bonds. The structure of the “head-to-head” dimer of β-CD was simulated byab initio calculations of the H-bonded dimer of α-d-glucose in the RHF/6-31G(d,p) approximation. In the dimer, both components are linked by a pair of H-bonds formed by the protons of the 3-OH groups and the O atoms of the, 2-OH groups. The dimerization energies obtained fromab initio and semiempirical MNDO/PM3 and AM1 calculations differ by about 2.5 times (8.6vs 3.2 and 3.8 kcal mol−1, respectively). 相似文献
14.
The geometries of acyclic and three-membered ring (nitroxide) H4C2NO radicals in their ground 2Π electronic states have been optimized completely at ab initio UHF and ROHF theoretical levels with the STO-3G and the 6-31G** basis sets. The optimizations favour the cyclic nitroxide
structure energetically. However ΔE(acyclic - cyclic) at the UHF and ROHF/6-31G** levels are only 3.2 and 1.9 kcal mol-1, respectively. Incomplete MP2/6-311G** optimizations support these results. The zero-point energy computed at the ROHF/6-31G**
level for the nitroxide radical is 2.5 kcal mol-1 higher than that for the acyclic structure, thus reversing the relative energies by 0.6 kcal mol-1. The energies of the two radical structures, relative to the sum of those for ethylene and NO, are very close to literature
values of the activation energies for the thermal, NO catalyzed geometrical isomerizations of olefins. Thus cyclic nitroxide
intermediates may play a role not only in the Hg 6(3P1) photosensitized, but also in the thermal, NO-catalyzed geometric isomerizations of olefins.
Paper dedicated to Professor Otto P. Strausz; presented in part at the 75th Canadian Chemical Congress and Exhibition, Edmonton,
May 31 – June 4, 1992. 相似文献
15.
Summary. Ab initio HF/6-31G* and MP2/6-31G*//HF/6-31G* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C
4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C
s) and twist (C
2h) conformers and requires about 22.3 kJ · mol−1. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol−1. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries
of the title compound are in good agreement with the results of ab initio methods.
Received July 9, 2001. Accepted September 26, 2001 相似文献
16.
Yu. A. Borisov Yu. A. Zolotarev E. V. Laskatelev N. F. Myasoedov 《Russian Chemical Bulletin》1997,46(3):407-409
The simplest quantum-chemical models of hydrogen spillover over a graphite-like surface as a proton or radical have been considered.
The condensed planar C24H12 molecule was used as a model surface. Theab initio calculations of the interaction of hydrogen with the model surface were carried out by the restricted Hartree-Fock (HF) method
in the STO-3G and 6-31 G* basis sets. The radical hydrogen can not bind to such a surface, whereas the proton binds to it with an energy release of
186 kcal mol−1. The activation energy of the transfer of the proton between two neighboring carbon atoms (10 kcal mol−1) has been determined. The simplest model of the hydrogen migration as a proton over the model surface can be used for describing
the spillover of hydrogen over the graphite surface.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 428–430, March, 1997. 相似文献
17.
Quantum-chemical calculations of the geometry and energies of nine possible isomers of 12-vertex cobaltacarborane CpCoC2B9H11 (1) were carried out by the DFT method (PBEPBE/DGDZVP/DGA1). Thermodynamic stability of the isomers increases with increasing
distance between the carbon atoms in the cage and is virtually independent of the position of the CpCo vertex. The relative
stabilities of the 1,2,3-(17.57 kcal mol−1), 1,2,4-(3.72 kcal mol−1), and 1,2,9-isomers of 1 (0 kcal mol−1) are similar to the corresponding values for the ortho (17.61 kcal mol−1), meta (3.21 kcal mol−1), and para isomers (0 kcal mol−1) of carborane C2B10H12. The results of the present study confirm a close similarity of the CpCo and BH fragments in metallacarborane chemistry.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1557–1559, July, 2005. 相似文献
18.
Quantum-chemical calculations have been carried out by the RHF/6-31G(d) and MP2/6-31+G(d) methods of molecules of N-chloromethylpyrrolidone,
N-chloromethylcaprolactam, N-chloromethyl-succinimide, and N-chloromethylphthalimide with full optimization of their geometry,
and also N-chloromethylpyrrolidone molecule by the RHF/6-31G(d) method at various angles of rotation of the CH2Cl group around the C―N bond. It was shown that the lower frequencies of the 35Cl NQR of the first two molecules in comparison with the later are mainly determined by the high populations of the p
σ
-orbitals of their Cl atoms. The population of the orbitals of the unshared electron pair of the N atom is practically unchanged
on rotating the CH2Cl group, but the N atom polarizes the C―Cl bond in the indicated molecule. This does not confirm the supposed p,σ*-conjugation in the Cl―C―N grouping.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1537–1544, October, 2008. 相似文献
19.
Ab initio calculations of the molecules of CH3- and CF3-substituted β-propiothiolactones and the productsof their deprotonation were carried out by the restricted Hartree—Fock method
with full geometry optimization using the 6–31 G* basis set. Peculiarities of the geometry and electronic structure of the systems in question were established. Only 2-methyl-β-propiothiolactone
forms a mesomeric stabilized carbanion in the case of proton abstraction from the α-position of thiolactone cycle. Carbanions
of 3-methyl, 2-, and 3-thrifluoromethyl-β-propiothiolactones are stabilized due to the ring opening to form ketene thiolate
ions. The CH-acidity of fluorine-containing β-thiolactones is much higher than that of nonfluorinated analogs (the differences
in the deprotonation energies are 13.4 to 25.2 kcal mol−1).
Deceased.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1719–1725, September, 1998. 相似文献
20.
The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted
Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation
about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of
PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular
to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol−1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998. 相似文献