共查询到20条相似文献,搜索用时 15 毫秒
1.
Maurice E. Schwartz Edward F. Hayes Stephen Rothenberg 《Theoretical chemistry accounts》1970,19(1):98-101
Nitrous acid, HONO, has been studied for three geometries by the ab initio LCAO SCF MO method with a basis of accurate gaussian atomic orbitals. The trans geometry is correctly predicted to be most stable, lying about 2 kcal/mole lower than the cis form, and 9 kcal/mole lower than the 90° form (experimental estimates being 0.4 and 11.6 kcal/mole, respectively). Population analysis, dipole moment components, and properties related to nuclear-nuclear and nuclear-electron potentials all show a partial breaking of the hydroxyl oxygen-nitrogen bond at 90° compared to cis and trans, as well as the effects of electronic rearrangement for nuclear screening in the high nuclear repulsion cis form. The cis to 90° barrier is dominated by the attractive components of the total energy, while the trans to 90° one is dominated by repulsive components, in agreement with our analysis and an earlier prediction by Allen. 相似文献
2.
F.F. Roelandt D.F. van de Vondel G.P. van der Kelen 《Journal of Molecular Structure》1981,76(2):187-195
The barriers to internal rotation have been computed by ab initio methods for CH3OCH3, CH3OSiH3 and SiH3OSiH3. It is shown that minimal basis set results agree fairly well with experimental results for CH3OCH3 and to a lesser extent for SiH3OSiH3. To predict a correct ordering of the CH3 and SiH3 rotation barriers in CH3OSiH3, a split valence basis set has to be used. Attention is also paid to the influence of geometry optimization on the barriers to internal rotation. 相似文献
3.
Rotation about N–CO bonds in amides has been extensively investigated, but a corresponding barrier to rotation about the P–CO bond in an acylphosphine has yet to be observed. In the present 4-31Gab initio study of formylphosphine, rotation barriers of 9.6 and 13.5 kJ mol–1 and a phosphorus pyramidal inversion barrier of 108.0 kJ mol–1 are predicted. A comparison of STO-3G and STO-3G* barriers suggests that polarization functions are not needed to describe rotation in this system.
Eine ab initio Untersuchung von Rotations- und Inversions-Barrieren in Formylphosphin
Zusammenfassung Die Rotation um N–CO-Bindungen in Amiden wurde bisher intensiv untersucht, eine entsprechende Rotationsbarriere für Drehungen um die P–CO-Bindung in Acylphosphinen wurde jedoch nicht beobachtet. Eine 4-31Gab initio-Untersuchung an Formylphosphin ergibt Rotationsbarrieren von 9,6 und 13,5 kJ mol–1 und eine pyramidale Inversionsbarriere von 108,0 kJ mol–1 als Voraussage. Ein Vergleich der STO-3G und STO-3G* Barrieren legt nahe, daß Polarisationsfunktionen für die Beschreibung der Rotation in diesen Systemen nicht nötig sind.相似文献
4.
U. A. Soliman 《Journal of Structural Chemistry》2016,57(1):76-89
The molecular structure of 1,3-dimethyluracil (C6H8N2O2; 1,3-DMU) is studied theoretically and experimentally using Gaussian 98 calculations and different spectroscopic techniques. The vibrational spectrum for 1,3-DMU in the solid phase is recorded in the IR range 4000-400 cm–1. Initially, in order to get the most stable structure, twelve structures were proposed for the titled compound as a result of the internal rotation of CH3 around C–N bonds and keto-enol tautomerism. The single point energy and frequency calculations are obtained by MP2 (Full) and DFT/B3LYP methods with the 6-31G(d) basis set using the Gaussian 98 computation package. After the complete relaxation of twelve isolated isomers, the (diketo) tautomer was the only favored structure owing to its low energy relative to the other isomers and the prediction of real frequencies. This interpretation is supported by the recorded infrared spectrum that shows the presence of only the diketo tautomer. Aided by the normal coordinate analysis and potential energy distributions, a confident vibrational assignment of the fundamental frequencies is calculated. The results are discussed herein and compared with similar molecules whenever possible. 相似文献
5.
Restricted rotation about the naphthalenylcarbonyl bonds in the title compounds resulted in mixtures of cis and trans rotamers, the equilibrium and the rotational barriers depending on the substituents. For 2,7-dimethyl-1,8-di-(p-toluoyl)-naphthalene (1) ΔH° = 3.66 ± 0.14 kJ mol?1, ΔS° = 1.67 ± 0.63 J mol?1 K?1, ΔH≠ct = 55.5 ± 1.3 kJ mol?1, ΔH≠ct = 51.9 ± 1.3 kJ mol?1, ΔS≠ct = ?41.3±4.1 J mol?1 K?1 and ΔS≠ct = ?42.9±4.1 J mol?1 K?1. The rotation about the phenylcarbonyl bond requires ΔH≠ = ?56.9±4.4 kJ mol?1 and ΔS≠ = ?20.5±15.3 J mol?1 K?1 for the cis rotamer, and ΔH≠ = 43.5Δ0.4 kJ mol?1 and ΔS≠ =± ?22.4Δ1.3 J mol?1 K?1 for the trans rotamer. The role of electronic factors is likely to be virtually the same for both these rotamers but steric interaction between the two phenyl rings occurs in the cis rotamer only. Hence, the difference of the activation enthalpies obtained for the cis and trans rotamers, ΔΔH?1 = 13.4 kJ mol?1, provides a basis for the estimation of the role of steric factors in this rotation. For the tetracarboxylic acid 2 and its tetramethyl ester 3 the equilibrium is even more shifted towards the trans form because of enhanced steric and electrostatic interactions between the substituents in the cis form. The barriers for the rotation around the phenylcarbonyl bond and the cis-trans isomerization are lowered; an explanation for this result is presented. 相似文献
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7.
Urs P. Wild Tae-Kyu Ha Guido A. Raggio Hans U. Keller Peter O. Brunner 《Helvetica chimica acta》1975,58(3):696-706
An ab initio SCF calculation of 42 points of the energy hypersurface of the fluoronium ion is presented using a contracted F(5s/3p), H(2s) gaussian basis set. In its equilibrium structure a bond length of 1.812 a.u. and a HFH bond angle of 127.2° are predicted. The calculated vibrational frequencies for H2F+, HDF+, and D2F+ are in good agreement with the experimental data. 相似文献
8.
9.
Solc R Lukes V Klein E Griesser M Kelterer AM 《The journal of physical chemistry. A》2008,112(43):10931-10938
In this paper, quantum chemical calculations for various cyano derivatives of thiophene and terthiophenes at the density functional theory (DFT) and ab initio M?ller-Plesset (MP2) levels of theory are presented. In the case of the studied terthiophenes, CN groups located in the central part of the molecule lead to a preference of cis-cis geometry over trans-trans conformation. For alpha-substituted dicyano terthiophene, the investigation of torsional dependences shows that the highest energy barrier occurs at the perpendicular orientation of the aromatic rings. On the other hand, the dicyano substitution in the central part of terthiophene molecule exhibits the lowest energy barrier. Excitation energies were calculated using time-dependent density functional theory (TD-DFT). The obtained theoretical results show that the CN groups in alpha and beta positions have a distinct effect on the excitation energies and corresponding oscillator strengths. A CN group located in the alpha position causes a larger bathochromic shift than a CN group in the beta position. Besides, a CN group in the beta position has negligible influence on the position of the first absorption maximum. 相似文献
10.
López-Martínez EI Rodríguez-Valdez LM Flores-Holguín N Márquez-Lucero A Glossman-Mitnik D 《Journal of computational chemistry》2009,30(7):1027-1037
It has been proved that fullerene derivatives, in which an oligophenylenevinylene (OPV) group is attached to C(60), present an interesting photophysical phenomenon and can be incorporated into photovoltaic cells. In these systems, the OPV acts as electron donor upon excitation, and then fullerene absorbs photoexcited electrons. These new organic semiconductor materials offer the prospect of lower manufacturing costs and they present several advantages: easy fabrication, large area, flexible and light weight devices when compared with inorganic counter parts. In the present theoretical study, oligomeric chains of p-phenylenevinylene (n-PPV, n = 3-8 units) and C(60)-OPV hybrids have been studied by density functional theory (DFT). Electronic properties such as electronic absorption and emission spectra were calculated in order to determinate how the increment of spectroscopic units affects their electronic behavior. These properties were carried out with time dependent-density functional theory (TD-DFT) and ZINDO semiempirical method. The theoretical calculations of the structural properties of n-PPV and fullerene-OPV hybrids were obtained using PBE1PBE/6-31G and ONIOM two-layered version, respectively. All calculations were done with Gaussian 03W program package. 相似文献
11.
C. Rigol C. Olea-Azar F. Mendizbal R. Briones H. Cerecetto M. Gonzlez 《Journal of Molecular Structure》2006,770(1-3):125-129
Theoretical studies of molecular conformations and electronic properties calculations of eight 5-nitrofuryl thiosemicarbazone free radicals, by means of ab initio (R/UHF), and DFT (R/UB3LYP) methods are presented and discussed in comparison with ESR and electrochemical experimental data. DFT calculated hyperfine coupling constants were used for the simulation of experimental spectra. We observed the molecules adopt mainly two conformations, both showing a pattern of spin density delocalization unusual for free radicals formed from aromatic nitrocompounds. Energy potential surfaces scaning through a determined dihedral angle were drawn to evaluate whether these conformations could coexist in equilibrium. Fukui and molecular orbital analysis were compared with ESR data as reactivity local indexes. 相似文献
12.
In view of a study of the atypical bases of the nucleic acids, the integral values appropriate for the methyl substituent have been determined in the SCF approximation previously described [1]. Both the inductive and the hyperconjugation effects have been introduced. An application to thymine is described. 相似文献
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14.
Jardillier N Berthomieu D Goursot A Reveles JU Köster AM 《The journal of physical chemistry. B》2006,110(37):18440-18446
The structural and electronic properties of the accessible Cu(I) site of a faujasite-type zeolite have been studied, by use of large cluster models and a density functional theory-based methodology. We demonstrate that the local ideal C(3) symmetry of the Cu(I) site II is broken. The Cu(I) cation is bonded to the zeolite framework by one bond of about 2.26 A and two shorter ones of 2.07 A. We demonstrate that only one cation position exists at this site. This result is also confirmed by a molecular electrostatic potential analysis. We show that local properties at site II, as well as the global properties of the solid (frontier orbitals), do not depend on the Al and cation distribution and only slightly on the cocation nature. Taking into account the present results and well-known experimental data, we propose that specific catalytic behaviors are correlated with local response properties, such as the local acid strength or, in other reactions, specific local architecture or confinement. 相似文献
15.
Wei-Xiu Pang Hong-Ye Wu Jian-Jun Zhao 《Phosphorus, sulfur, and silicon and the related elements》2019,194(1-2):69-75
The anharmonic force field and spectroscopy constants for CH2PCl are determined using CCSD(T), VPT2, and density functional theory employing cc-pVQZ basis sets. The molecule structure, rotational spectroscopic constants, and vibrational wave numbers are compared with the available experimental data. Anharmonicity constants, vibration-rotation interaction constants and cubic force constants are predicted. Vibrational wave numbers and rotational constants for CD2PCl are also determined using the same levels. The isotopic shifts of vibrational wave numbers are remarkable by D atom substitution for 1-chlorophosphaethene. 相似文献
16.
通过4种键连方式将苯环共价连接到超晶胞为1×1×3的锯齿型单壁碳纳米管CNT(8,0)上.在密度泛函理论基础上,通过Siesta软件计算苯环共价功能化碳纳米管的几何结构、能带结构、态密度和波函数,分析键连方式对碳纳米管电性的影响.结果表明苯环通过4种键连方式共价功能化的碳纳米管都是在Γ点具有直接带隙的半导体.其中直接键连和酰胺键连得到的苯环功能化碳纳米管在费米能级附近产生杂质带,比纯CNT带隙减小约0.4e V.而通过2个亚甲基键连和吡咯烷键连2种方式功能化的碳纳米管,其带隙仅比纯CNT带隙减小0.1~0.15e V. 相似文献
17.
Marilyn E. Jacox 《Chemical physics》1979,43(2):157-172
When methyl cyanide mixed with an excess of argon is codeposited at 14 K with a beam of argon atoms that has been excited by a low power microwave discharge, infrared and ultraviolet absorptions of several previously unidentified products appear. The most prominent set of absorptions is assigned to ketenimine, previously tentatively identified as the product of the reaction of NH with C2H2 in an argon matrix. Using a molecular geometry resulting from a recent ab initio calculation and a valence force field with four interaction constants, it has been possible to obtain a satisfactory least-squares force constant fit to the infrared data for seven isotopic species of ketenimine. Two electronic band systems are also reported for ketenimine, which is photodissociated by 2537-A radiation. The mechanism by which ketenimine is formed may involve an initial electron transfer from excited argon to methyl cyanide. Spectrospic data are also considered for the other products, one of them tentatively identified as CH2CH, which differ in their behavior on mercury-are photolysis of the sample. 相似文献
18.
P.L. Polavarapu 《Journal of computational chemistry》1993,14(6):751-752
Some force constants associated with the internal coordinates that sense handedness or chirality can have opposite signs in the enantiomers of chiral molecules. Examples of such force constants include interaction force constants between a torsional and stretching or bending internal coordinates. The sign reversal for these force constants in the enantiomers of chiral molecules or in opposite-handed molecular segments is best recognized by labeling them as chiral force constants. Recognition of chiral force constants suggests that certain guidelines are to be followed in the presentation of internal coordinate force constants. © 1993 by John Wiley & Sons, Inc. © John Wiley & Sons, Inc. 相似文献
19.
N. C. Bera I. Bhattacharyya A. K. Das 《International journal of quantum chemistry》2007,107(5):1067-1072
Ab initio and density functional methods are applied to study the spectroscopic constants and molecular properties of the diatomic cations He, Ne, Ar, HeNe+, and HeAr+. Among these cations, HeAr+ is found to be weakly bound and its spectroscopic constants are calculated using the Lennard‐Jones potential. The other molecules that are strongly bound obey Morse potential, and their spectroscopic constants are calculated accordingly. The calculated spectroscopic constants agree very well with the theoretical and experimental values wherever available. Most of the spectroscopic constants and molecular properties are reported for the first time. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
20.
Fuentes-Cabrera M Sumpter BG Sponer JE Sponer J Petit L Wells JC 《The journal of physical chemistry. B》2007,111(4):870-879
M-DNA is a type of metalated DNA that forms at high pH and in the presence of Zn, Ni, and Co, with the metals placed in between each base pair, as in G-Zn-C. Experiments have found that M-DNA could be a promising candidate for a variety of nanotechnological applications, as it is speculated that the metal d-states enhance the conductivity, but controversy still clouds these findings. In this paper, we carry out a comprehensive ab initio study of eight G-Zn-C models in the gas phase to help discern the structure and electronic properties of Zn-DNA. Specifically, we study whether a model prefers to be planar and has electronic properties that correlate with Zn-DNA having a metallic-like conductivity. Out of all the studied models, there is only one which preserves its planarity upon full geometry optimization. Nevertheless, starting from this model, one can deduce a parallel Zn-DNA architecture only. This duplex would contain the imino proton, in contrast to what has been proposed experimentally. Among the nonplanar models, there is one that requires less than 8 kcal/mol to flatten (both in gas and solvent conditions), and we propose that it is a plausible model for building an antiparallel duplex. In this duplex, the imino proton would be replaced by Zn, in accordance with experimental models. Neither planar nor nonplanar models have electronic properties that correlate with Zn-DNA having a metallic-like conductivity due to Zn d-states. To understand whether density functional theory (DFT) can describe appropriately the electronic properties of M-DNAs, we have investigated the electronic properties of G-Co-C base pairs. We have found that when self-interaction corrections (SIC) are not included the HOMO state contains Co d-levels, whereas these levels are moved below the HOMO state when SIC are considered. This result indicates that caution should be exercised when studying the electronic properties of M-DNAs with functionals that do not account for strong electronic correlations. 相似文献