共查询到20条相似文献,搜索用时 909 毫秒
1.
The ab initio and density functional (DFT) methods were performed on binary systems of N,N-dimethylformamide (DMF) with xylenes (o-, or m-, or p-xylene), and seven stable configurations were obtained with no imaginary frequencies. To obtain the interaction energies
of these complexes, single-point energy calculations with basis set superposition error (BSSE) correction were carried out
at B3LYP/6-31G* and MP2/6-31G* levels. The structures, Chelpg (charges from electrostatic potentials using a grid-based method)
charge distribution and bond characteristics of the mentioned complexes were calculated. The results indicated the presence
of double C–H···O hydrogen bonds between DMF and xylenes in these complexes and the interaction energies of hydrogen bonding
between DMF and xylene systems decreased in the following sequence: DMF–o-xylene: a1 > DMF–m-xylene: b1 > DMF–p-xylene: c1. 相似文献
2.
The structure and conformational behavior of 1: 1 molecular assotsiates of 2-methyl-1,3,2-oxazaand 2-methyl-1,3,2-oxathiaborinanes
with water were studied ab initio in terms of HF/6-31G(d) and PBE/3z quantum-chemical approximations. The most stable complexes are formed via hydrogen bonding with the heteroatoms
(oxygen and nitrogen or sulfur). Their conformational behavior implies equilibrium between sofa and half-chair conformers, and intermolecular hydrogen bond is retained in the course of ring interconversion. No associate with a dative
O→B bond is formed. 相似文献
3.
The hydrogen-bonded structures of the CH3OH complexes with CF4, C2F2, OC, Ne, and He are designated as the starting points for geometry optimizations without and with counterpoise (CP) correction
at MP2 level of theory with the basis sets 6-31+G*, 6-31++G**, and 6-311++G**, respectively. Tight convergence criteria are
applied throughout all geometry optimizations in order to reduce the computational errors. According to the optimizations
without CP correction, a blue-shifted O–H···Y (where Y = F, O, Ne, or He) hydrogen bond exists in all these five complexes.
The magnitudes of blue shifts of ν(O–H) of the former four complexes with respect to that of CH3OH are reduced greatly when the polarization and diffuse functions of the hydrogen atoms are added (results from 6-31+G* versus
those from 6-31++G**). However, for the complexes CH3OH–CF4 and CH3OH–C2F2, our optimizations using the CP corrections did not find the hydrogen-bonded structure to be a stationary point. The energy
minimum of both the complexes corresponds to a non-hydrogen-bonded structure. 相似文献
4.
A density functional theory (DFT) investigation on novel sandwich-type D
5 [C5Li5]Mg
n
[C5Li5] (n = 2–8) complexes containing –Mg–Mg– chain has been performed in this work. The equilibrium geometries, electronic structures,
vibrational frequencies, and stabilities of these complexes are researched by B3LYP and BP86 methods at 6-311+G(d) levels
of theory. The Mg
n
2+ sandwich complexes with D
5 symmetry are all true minima on the potential energy surface. NBO analyses for the series of complexes reveal that the Mg–Mg
bond is a weak σ covalent bond. There are mainly electrostatic interactions between C5Li5
− ligands and Mg
n
2+(n = 2–8) nuclear in these complexes. The NICS and NICSzz computed with GIAO-B3LYP/6-311+G(d) indicates that the C5Li5
− rings in the series of complexes are aromatic. These novel complexes turn out to be strongly thermodynamically favored in
the gas phases and may be targeted in future experiments to expand the structural domain of sandwich-type complexes. 相似文献
5.
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
6.
Krivoruchka I. G. Vokin A. I. Turchaninov V. K. 《Russian Journal of Organic Chemistry》2002,38(10):1456-1461
According to the results of HF/6-31G* and B3LYP/6-31G* nonempirical calculations, N-(4-methyl- 2-nitrophenyl)acetamide in the synperiplanar and antiperiplanar conformations gives stable complexes with protophilic solvents, which are stabilized by bifurcated (three-center) hydrogen bond. The complexes are characterized by (1) opposite variations of the interatomic distances and angles corresponding to intra- and intermolecular components of the bifurcated hydrogen bond, (2) extension of the intramolecular component and a more pronounced shortening of the intermolecular component with increase in the strength of the three-center H-complex, and (3) nonlinear and nonmonotonic relation between the NH stretching vibration frequency and the energy of complex formation. 相似文献
7.
L. P. Oznobikhina N. N. Chipanina T. N. Aksamentova B. A. Shainyan 《Russian Journal of General Chemistry》2009,79(8):1674-1682
According to the data of quantum chemical calculations using the DFT method (B3LYP/6-311G*), dimethylsulfone (I), N,N-dimethylmethanesulfonamide (II) and N,N-dimethyltrifluoromethanesulfonamide (III) form with methanol and phenol H-complexes of two types: (1) having nonlinear structure
and (2) bidentate complexes with participation of both oxygen atom lone pairs in the formation of the H-bond. The angle determining
the directionality of the hydrogen bond with respect to the axis of the nearest lone electron pair of the SO2 group oxygen atom in the conformational isomers of these complexes falls within the range 3°–100°. Variation of the calculated
values of Δν(OH) in the H-complexes is parallel to that observed in their IR spectra and reflects the decrease of basicity
of the sulfonyl group in the order I > II > III. 相似文献
8.
Yordanka Dimitrova Sigrid D. Peyerimhoff 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,32(3):241-247
The hydrogen-bonded complexes involving formaldehyde and a series of proton donors of varying strengths, have been investigated at different levels of ab initio MO theory. The structures of the studied complexes were SCF optimized at the 6-31G basis set level. The binding energy was estimated employing basis set superposition correction, zero-point vibrations and MP2 correlation contribution at the different basis set: STO-3G; 6-31G; MP2/6-31G; 6-31G**; MP2/6-31G**; 6-311G(2d, 2p) and MP2/6-311G(2d, 2p). Linear relationships were found of the calculated binding energy with: the calculated shift in the carbonyl stretching frequency, the changes in carbonyl bond length and the optimum value of hydrogen-bond distance; furthermore the calculations confirm a parallel trend between the proton-donor ability and the strength of the hydrogen bond. 相似文献
9.
The complexes formed via hydrogen bonding interactions between cysteine and propanoic acid have been studied at the density
three-parameter hybrid functional DFT-B3LYP/6-311++G(d,p) level regarding their geometries, energies, vibrational frequencies,
and topological features of the electron density. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital
(NBO) analysis was employed to elucidate the interaction characteristics in cysteine–propanoic acid (Cys–Prop) complexes.
More than 10 kinds of hydrogen bonds (H-bonds) including intra- and inter-molecular H-bonds have been found in Cys–Prop complexes.
The results show that both the strength of H-bonds and the deformation are important factors for the stability of Cys–Prop
complexes. The strongest H-bonds (O2HA···O1B and O2HA···O1B) exist in the most stable Cys–Prop complex. The stronger H-bonds formed between hydroxyl and O (or N) atom usually stronger
than those involve C (or S) atom. Relationships between the electron density (ρ) of BCP and H-bond length as well as the Fock matrix element (F
ij) has also been investigated and used to study the nature of H-bonds. Moreover, the results show that the change of the bond
length linearly correlates with the corresponding frequency shift. 相似文献
10.
Calculation of the hydrogen binding energies of complexes between formamide and adenine-thymine pair
Chun-sheng Duan Hui Fu Jin-mao You Ke-sheng Ma Zheng-yu Zhou 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(13):2300-2305
The hydrogen bonding of complexes formed between formamide and adenine-thymine base pair has been completely investigated
in the present study. In order to gain deeper insight into structure, charge distribution, and energies of complexes, we have
investigated them using density functional theory at 6–311++G(d, p), 6–31G, 6–31+G(d), and 6–31++G(d, p) level. Seven stable cyclic structures (ATF1–ATF7) being involved in the interaction has been found on the potential energy
surface. In addition, for further correction of interaction energies between adenine—thymine and formamide, the basis set
superposition error associated with the hydrogen bond energy has been computed via the counterpoise method using the individual
bases as fragments. The infrared spectrum frequencies, IR intensities and the vibrational frequency shifts are reported. 相似文献
11.
Xin Ren Zhouyang Luo Jinpei Du Shi Wu 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(5):826-830
Theoretical investigation on the stabilities and spectroscopic properties of the complexes formed by cyciobis(paraquat-p-anthracene) with pharmaceutical molecules were performed using the semi-empirical PM3 and B3LYP/3-21G methods. Based on the
B3LYP/3-21G optimized geometries, the energies of the complexes were calculated at B3LYP/6-31G(d) level. The binding energies of the complexes were computed after the correction of basis set superposition error (BSSE).
The energy gaps of the complexes are decreased due to the formation of the hydrogen bonds. The stretching vibrations of the
C-H bonds adjacent to the hydrogen bonds in the IR spectra of the complexes calculated with PM3 method are red-shifted compared
with those of the host. The chemical shifts of α-C and β-C atoms in the complexes calculated at B3LYP/3-21G level are shifted
downfield due to the formation of the hydrogen bonds and the electron-withdrawing effect of the nitrogen atoms. The aromaticities
of the complexes are improved because of the enlargement of the conjugation system and the overlap of electron cloud based
on the nuclear independent chemical shifts (NICS) calculated at B3LYP/3-21G level. 相似文献
12.
S. E. Boganov V. I. Faustov M. P. Egorov O. M. Nefedov 《Russian Chemical Bulletin》1998,47(6):1054-1060
Complexes of difluorostannylene with dinitrogen of composition 1∶1 and 1∶2 were stabilized in Ar matrix (12 K) and characterized
by IR spectra. The bands at 588, 565, and 583, 557 cm−1, respectively, were assigned to these complexes. Potential energy surfaces of the systems SnF2+N2 and SnF2+2N2 were studied by theab initio MP2/3-21G(d2)//HF/3-21G(d2) method using the basis set including polarization functions at Sn, F, and N atoms. Equilibrium
structures of the complexes haveC
s andC
2v symmetry and correspond to coordination of lone electron pairs of nitrogen molecules with vacant p-AO of the carbenic center.
The calculated complexation energies are equal to 4.6 and 8.9 kcal mol−1, respectively. Based on results of quantum-chemical calculations an interpretation of the IR spectra of the complexes was
given and it was shown that cycloaddition of SnF2 to a triple N≡N bond with formation ofcyclo-SnF2N2 is energetically unfavorable. The absorption band belonging to SiF4·N2 complex in Ar matrix was detected and assigned.
Dedicated to the memory of Academician M. E. Vol'pin timed to his 75th birthday.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1087–1093, June, 1998. 相似文献
13.
Thahira B. S. A. Ravoof Karen A. Crouse M. Ibrahim M. Tahir Fiona N. F. How Rozita Rosli David J. Watkins 《Transition Metal Chemistry》2010,35(7):871-876
A tridentate nitrogen-sulfur Schiff base, 3-methylbenzyl 2-(6-methylpyridin-2-ylmethylene)hydrazine carbodithioate (6mpyS3M),
was synthesized by condensation of 6-methylpyridine-2-aldehyde with S-3-methylbenzyldithiocarbazate. It crystallized in space
group P 21/n. It displayed intermolecular N–H···N hydrogen bonding between the α-nitrogen and the pyridyl nitrogen. The thione sulfur is in a trans position with respect to the 6-methylpyridine fragment across the C–N bond but adopts a cis position with the 3-methylbenzyl fragment through the C–S bond. Octahedral complexes containing two 6mpyS3M ligands were
prepared with Cu(II), Ni(II), Zn(II) and Cd(II). 6mpyS3M and its metal complexes were assayed against selected microbes and
two breast cancer cell lines. 6mpyS3M was strongly active against both cancer cell lines. Its metal complexes showed high
selectivity with Cu(II), Ni(II) and Zn(II) complexes strongly active against only one of the cancer cell lines, whereas the
Cd(II) complex was strongly active only against the other. Only Cu(II) and Cd(II) complexes were active against some of the
bacteria. 相似文献
14.
The stability of hydrogen-bonded complexes, DMF–H
n
CCl4−n
(n = 1–3), has been investigated by several theoretical methods including the MP2 level of ab initio theory at various basis
sets from 6-31+G* to 6-311++G**. Two stable configurations (respectively a and b) were obtained for each complex with no imaginary frequencies. The minimum energy structure of these complexes has also been
analyzed by means of the atoms in molecule theory at MP2/6-311++G** level. It is found that C–H···O hydrogen bonding exists
in these systems and that the intensity of HB interaction gradually increases with successive chlorination. Computed results
indicate that these complexes automatically assemble into different stable configurations. For the complexes under consideration,
their stabilities can be mainly ascribed to the intermolecular HB interaction. The present work is helpful to clearly understand
the interaction mechanism of these complexes in theory. 相似文献
15.
Pu Su Zhao Ji Ming Xu Wei Guang Zhang Fang Fang Jian Lan Zhang 《Structural chemistry》2007,18(6):993-1000
The title compound of 3-p-methylphenyl-4-amino-1, 2, 4-triazole-5-thione was synthesized and characterized by elemental analysis, IR, electronic spectra,
and X-ray single crystal diffraction. Quantum chemical calculations of the structure, natural bond orbital, and thermodynamic
functions of the title compound were performed by using B3LYP/6-311G** and HF-6-311G** methods. Both the methods can well
simulate the molecular structure. Vibrational frequencies were predicted, assigned and compared with the experimental values,
and B3LYP/6-311G** method is superior to HF/6-311G** method to predict the vibrational frequencies. Electronic absorption
spectra calculated by B3LYP/6-311G** method have some red shifts compared with the experimental ones and natural bond orbitals
analyses indicate that the two absorption bands are mainly derived from the contribution of n → π* and π → π* transitions. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures
have been calculated, revealing the correlations between C
0
p,m
, S
0
m
, H
0
m
, and temperatures. 相似文献
16.
A. S. Saghiyan L. L. Manasyan S. A. Dadayan S. G. Petrosyan A. A. Petrosyan V. I. Maleev V. N. Khrustalev 《Russian Chemical Bulletin》2006,55(3):442-450
NiII complexes with the Schiff bases of (E)-and (Z)-2-aminobut-2-enoic acids were obtained with (S)-N-(2-benzoylphenyl)-1-(2-chlorobenzyl)pyrrolidine-2-carboxamide and (S)-N-(2-benzoylphenyl)-1-(3,4-dimethylbenzyl)pyrrolidine-2-carboxamide as new chiral auxiliaries. Asymmetric addition of nucleophiles
to the C=C bond of these complexes was studied.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 428–435, March, 2006. 相似文献
17.
A systematic study on the structural characteristics of the 2-pyranone ring containing molecules with bromine, nitrile, and
amide substituents at the C-3 position in the ring is conducted in the electronic ground (S
0) state by DFT calculations using the B3LYP/6-311++G** method. The geometrical structure of the bromine substituted compound,
which shows potent hepatoprotective activity, is studied both in the ground (S
0) and first excited singlet (S
1) states using RHF/6-311++G** and CIS/6-311++G** methods respectively. The molecules are found to exist in two isomeric forms
gauche and trans that have the enthalpy difference of less than 3.32 kcal/mol; the latter is the preferred orientation in the gaseous phase.
The S
1 state is a 1(π,π*) state that arises π-electron transfer from the region of a double bond in the pyranone ring to the region of the internuclear
bond connecting the 2-pyranone and benzene rings. A complete vibrational analysis is conducted for the 3-bromo-6-(4-chlorophenyl)-4-thiomethyl-2H-pyran-2-one
molecule based on the experimental infrared spectra in the 50–4000 cm−1 region and DFT/6- 311++G** computations of vibrational frequencies for the gauche and trans isomeric forms. Spectral assignments based on the potential energy distribution along the internal coordinates confirm the
nonplanar structure of the molecule. 相似文献
18.
Theoretical study on the binding affinities of dehydrotetrapyrido[20] annulene to the alkene and aromatic molecules was performed
using the AM1 and DFT methods. It indicated that the host possesses the ability to bind the above molecules since the binding
energies of the complexes were negative. The complexes were stabilized via the hydrogen bonding, static effect, and π — π stacking interaction between the host and guest molecules. Based on the B3LYP/3-21G
optimized geometries, the electronic, IR, and NMR spectra were calculated using the INDO/CIS, AM1, and B3LYP/3-21G methods,
respectively. Due to the hydrogen bonding, the first absorption maxima in the electronic spectra of studied complexes were
blue-shifted, whereas the main IR frequencies for some of the complexes were red-shifted. At the same time, the chemical shifts
of carbon atoms forming the
bonds in the complexes were lower, compared to those of the host. 相似文献
19.
在DFT-B3LYP/6-311++G**水平下求得CH3SH…HOO复合物势能面上的稳定构型. 计算结果表明, 在HOO以其O8—H7作为质子供体与CH3SH分子中的S5原子为质子受体形成的氢键复合物1和2中, O8—H7明显被“拉长”, 且其伸缩振动频率发生显著的红移, 红移值分别为330.1和320.4 cm-1; 在CH3SH分子以其S5—H6作为质子供体与HOO的端基O9原子为质子受体形成的氢键复合物3和4中, 也存在类似的情况, 但S5—H6伸缩振动频率红移不大. 经MP2/6-311++G**水平计算的4种复合物含BSSE校正的相互作用能分别为-20.81, -20.10, -4.46和-4.52 kJ/mol. 自然键轨道理论(NBO)分析表明, 在CH3SH…HOO复合物1和2中, 引起H7—O8键长增加的因素包括两种电荷转移, 即孤对电子n1(S5)→σ*(H7—O8)和孤对电子n2(S5)→σ*(H7—O8), 其中后者为主要作用. 在复合物3和4中也有相似的电荷转移情况, 但轨道间的相互作用要弱一些. AIM理论分析结果表明, 4个复合物中的S5…H7间和O9…H6间都存在键鞍点, 且其Laplacian量▽2ρ(r)都是很小的正值, 说明这种相互作用介于共价键和离子键之间, 偏静电作用为主. 相似文献
20.
Ab initio molecular orbital calculations were used to study hydrogen bonding interactions and interatomic distances of a number of hydrogen bonded complexes that are germane to biomolecular structure and function. The calculations were carried out at the STO-3G, 3-21G, 6-31G*, and MP2/6-31G* levels (geometries were fully optimized at each level). For anionic species, 6-31 + G* and MP2/6-31 + G* were also used. In some cases, more sophisticated calculations were also carried out. Whenever possible, the corresponding enthalpy, entropy, and free energy of complexation were calculated. The agreement with the limited quantity of experimental data is good. For comparison, we also carried out semiempirical molecular orbital calculations. In general, AM1 and PM3 give lower interaction enthalpies than the best ab initio results. With regard to structural results, AM1 tends to favor bifurcated structures for O? H-O and N? HO types of hydrogen bonds, but not for hydrogen bonds involving O-H? S and S-H? O, where the usual hydrogen bond patterns are observed. Overall, AM1 geometries are in general in poor agreement with ab initio structural results. On the other hand, PM3 gives geometries similar to the ab initio ones. Hence, from the structural point of view PM3 does show some improvement over AM1. Finally, insights into the formation of cyclic or open formate–water hydrogen bonded complexes are presented. © 1992 by John Wiley & Sons, Inc. 相似文献