Theoretical Studies on the Coplanar Dicage Pentaprismane C16H12

1 INTRODUCTION A series of hydrocarbons of polyhedral shapes or cages, such as cubane and dodecahrane[1], have been synthesized. Each of these molecules has only one cage. It is well known that every carbon atom can form four bonds with other atoms, and …     

DFT and ab initio calculations on two reactions between hydrogen atoms and the fire suppressants 2-H heptafluoropropane and CF3Br

Reaction enthalpies and barrier heights of the reactions CF3Br+H-->CF3+HBr {reaction (1)} and CF3CHFCF3+H-->CF3CFCF3+H2 {reaction (2)} have been calculated at the near state-of-the-art ab initio level, and also by employing the B3LYP, BH&HLYP, BB1K, MPW1K, MPWB1K and TPSS1KCIS functionals. In addition, the integrated molecular orbital+molecular orbital (IMOMO) method has been used to study reaction (2). The ab initio benchmark values of the reaction enthalpy (298 K) and barrier height (0 K) of reaction (2) are reported for the first time {-(0.7+/-0.7) and 13.3+/-0.5 kcal/mole respectively}. When density functional theory (DFT) results are compared with ab initio benchmarks for both reactions (1) and (2), the MPWB1K functional is found to have the best performance of the six functionals used. The IMOMO method with the RCCSD/aug-cc-pVTZ and/or RCCSD(T)/aug-cc-pVTZ levels, as the high levels of calculation on the model system, gives reaction enthalpies and barrier heights of reaction (2), which agree with ab initio benchmark values to within 1 kcal/mole. Computed key geometrical parameters and imaginary vibrational frequencies of the transition state structures of reactions (1) and (2) obtained at different levels of calculation are compared. The magnitudes of the computed imaginary vibrational frequencies of the transition states of both reactions considered are found to be very sensitive to the levels of calculation used to obtain them. The heat of formation (298 K) of CF3CFCF3 calculated at the near state-of-the-art level has a value of -(318+/-3) kcal/mole.     

Ab initio and DFT studies of the molecular structures and vibrational spectra of succinonitrile

The Molecular structure, conformational stability and vibrational frequencies of succinonitrile NCCH2CH2CN have been investigated with ab initio and density functional theory (DFT) methods implementing the standard 6-311++G* basis set. The potential energy surfaces (PES) have been explored at DFT-B3LYP, HF and MP2 levels of theory. In agreements with previous experimental results, the molecule was predicted to exist in equilibrium mixture of trans and gauche conforms with the trans form being slightly lower in energy. The vibrational frequencies and the corresponding vibrational assignments of succinonitrile in both C2h and C2 symmetry were examined theoretically and the calculated Infrared and Raman spectra of the molecule were plotted. Observed frequencies for normal modes were compared with those calculated from normal mode coordinate analysis carried out on the basis of ab initio and DFT force fields using the standard 6-311++G* basis set of the theoretical optimized geometry. Theoretical IR intensities and Raman activities are reported.     

Theoretical studies of the reactions of O(~3p) with halogenated methyl (Ⅰ)——Reaction mechanism of the O(~3p) CH_2Cl reaction

The reaction of O(~3P) with CH_2Cl radical has been studied using ab initio molecular orbital theory. G2 (MP2) method is used to calculate the geometrical parameters, vibrational frequencies and energies of various stationary points on the potential energy surface. The reaction mechanism is revealed. The addition of O(~3P) with CH_2Cl leads to the formation of an energy rich intermediate OCH_2Cl which can subsequently undergo decomposition or isomerization to the final products. The calculated heat of reaction for each channel is in agreement with the experimental value. The production of H CHClO and Cl CH_2O are predicted to be the major channels. The overall rate constants are calculated using transition state theory on the basis of ab initio data. The rate constant is pressure independent and exhibits negative temperature dependence at lower temperatures, in accordance with the experimental results.     

Synthesis and Electronic Properties of 6-Chloro-2-diethylaminoethyl-3(2H)-pyridazinone

6-Chloro-2-diethylaminoethyl-3(2H)-pyridazinone was synthesized by the reaction of 6-chloro-3(2H)-pyridazinone and 2-diethylamionethyl chloride reaction in methylbenzene.Then the structure was characterized by means of ^1H NMR,IR,UV.By the method of ab initio HF and density functional theory(DFT) BeLYP,the geometric structures of the reagent intermediate,the product and its isomer were optimized and their total energies were calculated,The properties for the frontier molecular orbitals and the rules for energy distribution were analyzed systematically.It was shown that the energy of the nitrogen alkyl compound is lower than that of the oxy alkyl compound and the former is stable than the latter.This result is in accordance with the fact that 6-chloro-2-diethylaminoethyl-3(2H)-pyridazinone is synthesized by the reaction of 6-chloride-2-diethylaminoethyl-3(2H)-pyridazinone and 2-diethylaminoethyl chloride.     

Theoretical investigation of the structure and vibrational spectra of carbamoyl azide

Molecular structure and vibrational frequencies of carbamoyl azide NH2CO-NNN have been investigated with ab initio and density functional theory (DFT) methods. The molecular geometries for all the possible conformers of the molecule were optimized using DFT-B3LYP, DFT-BLYP and MP2 applying the standard 6-311++G** basis set. From the calculations, the molecule was predicted to exist predominantly in cis conformation with the cis-trans rotational barrier of about 7.91-9.10 kcal/mol depending on the level of theory applied. The vibrational frequencies and the corresponding vibrational assignments of carbamoyl azide in Cs symmetry were examined theoretically and the calculated Infrared and Raman spectra of the molecule in the cis conformation were plotted. Observed frequencies for normal modes were compare with those calculated from normal mode coordinate analysis carried out on the basis of ab initio and DFT force fields using the standard 6-311++G** basis set of the theoretical optimized geometry. Theoretical IR intensities and Raman activities are reported.     

FTIR and FT-Raman spectra, assignments, ab initio HF and DFT analysis of xanthine

The molecular vibrations of xanthine were investigated in polycrystalline sample, at room temperature by Fourier transform infrared (FTIR) and FT-Raman spectroscopies. The spectra of the molecule have been recorded in the regions 4000-50 cm(-1) and 3500-100 cm(-1), respectively. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of ab initio Hartree-Fock (HF) and density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from ab initio and DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy have been calculated for the molecule. Unambiguous vibrational assignment of all the fundamentals was made using the potential energy distribution (PED).     

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one by Hartree-Fock and density functional theory calculations

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one (C(11)H(13)N(3)O(2)) in the ground state have been investigated by Hartree-Fock and density functional method (B3LYP and BLYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of title compound and calculated results by HF and DFT methods indicate that B3LYP is superior to the scaled HF approach for molecular problems.     

B(C2H5)2q及其衍生物电子光谱性质的密度泛函理论研究

采用密度泛函理论(DFT)B3LYP、abinitioHF和单激发组态相互作用(CIS)等方法分别优化了有机配合物B(C2H5)2q及其衍生物的基态及最低激发单重态几何结构.用含时密度泛函理论(TD-DFT)对B(C2H5)2q及其衍生物的电子光谱进行了研究.发现该类物质是配体发光配合物,其发光源于8-羟基喹啉配体内π*     

Spectroscopic analysis of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile

The optimized geometry and vibrational frequencies of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile (DOPNA) were obtained by ab initio DFT/B3LYP level with complete relaxation in the potential energy surface using 6-31G and 6-311G basis sets. The Fourier-transform infrared (FT-IR) spectrum of DOPNA has been recorded in the region 4000-400 cm(-1). The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The calculated frequencies are in comparable agreement with the experimental frequencies. The calculated energy span between the HOMO and the LUMO of DOPNA is 2.94 and 2.87eV by B3LYP/6-31G and B3LYP/6-311G, respectively.     

Ab initio HF, DFT and experimental (FT-IR) investigation of vibrational spectroscopy of P-N,N-dimethylaminobenzylidenemalononitrile (DBM)

The optimized geometry and vibrational frequencies of P-N,N-dimethylaminobenzylidenemalononitrile (DBM) were obtained by ab initio HF and DFT/B3LYP levels with complete relaxation in the potential energy surface using 6-31++G(d,p) and 6-311++G(d,p) basis sets. The Fourier-transform infrared (FT-IR) spectrum of DBM has been recorded in the region 4000-400 cm(-1). The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The calculated frequencies are in good agreement with the experimental frequencies.     

Vibrational spectroscopy (FTIR and FTRaman) investigation using ab initio (HF) and DFT (B3LYP) calculations on the structure of 3-Bromo phenol

The FT-IR and FT-Raman spectra of 3-Bromo phenol (3-BP) molecule have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1). The molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-fock (HF) and DFT (B3LYP) methods with 6-31G (d, p) and 6-311G (d, p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. Making use of the recorded data, the complete vibrational assignments are made and analysis of the observed fundamental bands of molecule is carried out. The geometries and normal modes of vibrations obtained from ab initio HF and B3LYP calculations are in good agreement with the experimentally observed data. The differences between the observed and scaled wave number values of most of the fundamentals are very small in DFT than HF. The inductive effect of halogen atom in the molecule has also been investigated.     

Vibrational assignment, structure and intramolecular hydrogen bond of 4-methylamino-3-penten-2-one

The molecular structure, intramolecular hydrogen and vibrational frequencies of 4-methylamino-3-penten-2-one were investigated by a series of density functional theoretical (DFT) calculations and ab initio calculation at the post-Hartree-Fock (MP2) level. Fourier transform infrared and Fourier transform Raman spectra of this compound and its deuterated analogue were clearly assigned. The calculated geometrical parameters show a strong intramolecular hydrogen bond with a N...O distance of 2.622-2.670 A. This bond length is about 0.02 A shorter than that in its parent, 4-amino-3- penten-2-one which is in agreement with spectroscopic results. Furthermore, the conformations of methyl groups with respect to the plane of the molecule and with respect to each other were investigated.     

Theoretical Study on the Structure and Vibrational Spectra for4-methyl-3-penten-2-one

The4-methyl-3-penten-2-oneisanimportanta,0-unsaturedketonemoleculeandanimportantligandoftheorganometalliccompounds.Untilnow,somepropertiesofphoto-chemistryandexcitedstateshavebeenexperimentallystudied'-#andconformationofthemoleculewerealsostudiedinexperiments"'.Standardinfraredgratingspectrumwasalsoobtainedin1970'.However,therearenodensityfunctionaltheory(DFT)calculationsofthismoleculeintheliterature.Recently,densityfunctionaltheoryhasbeenacceptedbytheahinitioquantumchemistrycommunityasacost…     

Vibrational spectroscopy investigation using ab initio and density functional theory analysis on the structure of 2-amino-4,6-dimethoxypyrimidine

The FTIR and FT-Raman spectra of 2-amino-4,6-dimethoxypyrimidine (2A46DMP) has been recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2A46DMP were obtained by the ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311G(d,p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.     

Ne-HCl势能面和振转光谱的理论研究

利用量子化学计算方法CCSD(T)和大基组aug-cc-pVTZ加键函数3_s3_p2_d对Ne-HCl体系的分子间势能面进行了理论研究.结果表明,势能面上有两个势阱,分别对应于线性Ne-ClH和Ne-HCl构型.通过精确求解核运动方程发现,该从头算势能面分别支持5个(对Ne-HCl)和7个(Ne-DCl)振动束缚态.计算得到的振转跃迁频率与实值值吻合.     

Vibrational spectroscopy (FT-IR and FT-Raman) investigation, and hybrid computational (HF and DFT) analysis on the structure of 2,3-naphthalenediol

The FT-IR and FT-Raman vibrational spectra of 2,3-naphthalenediol (C(10)H(8)O(2)) have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1) in solid phase. A detailed vibrational spectral analysis has been carried out and the assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-Fock (HF) and DFT (LSDA and B3LYP) methods with 6-31+G(d,p) and 6-311+G(d,p) basis sets. There are three conformers, C1, C2 and C3 for this molecule. The computational results diagnose the most stable conformer of title molecule as the C1 form. The isotropic computational analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and DFT methods. Comparison of the simulated spectra provides important information about the capability of computational method to describe the vibrational modes. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and Frontier molecular orbital energies, are performed by time dependent DFT approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated. The statistical thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) and their correlations with temperature have been obtained from the theoretical vibrations.     

FTIR, FT-Raman spectra and ab initio DFT vibrational analysis of 2-bromo-4-methyl-phenylamine

The FTIR and FT-Raman spectra of 2-bromo-4-methyl-phenylamine (BMP) have been recorded. From the standard geometrical parameters the geometry of BMP was optimized at ab initio and DFT levels of theory with complete relaxation in the potential energy surface using 6-311+g(d,p) and 6-311+g(2df,2p) basis sets. Several thermodynamic parameters were also calculated for the minimum energy conformer at ab initio and DFT level of theories. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. Majority of the computed wavenumbers were found to be in good agreement with the experimental observations. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.     

2-甲基-6-二乙胺基乙氧基-3(2H)-哒嗪酮的合成及其电子性质

分别利用两种方法合成2－甲基－6－二乙胺基乙氧基－3（2H）－哒嗪酮，用^1H NMR,IR,UV和MS进行结构表征，利用ab initio HF和密度泛函理论（DFT）B3LYP方法，对反应物、中间物、产物及其同分异构体进行几何结构的优化和总能量计算，系统分析前线分子轨道特征和能级分布规律，结果表明，2－甲基－6－二乙胺基乙氧基－3（2H）－哒嗪酮比其同分异构体哒嗪氮烷基化合物的能量低，前比后稳定，与实验事实相符合。     

Ab initio and DFT studies of the vibrational spectra of hydrogen-bonded PhOH...(H2O)4 complexes

The vibrational characteristics (vibrational frequencies and infrared intensities) for the hydrogen-bonded complex of phenol with four water molecules PhOH...(H2O)4 (structure 4A) have been predicted using ab initio and DFT (B3LYP) calculations with 6-31G(d,p) basis set. The changes in the vibrational characteristics from free monomers to a complex have been calculated. The ab initio and B3LYP calculations show that the observed four intense bands at 3299, 3341, 3386 and 3430 cm(-1) can be assigned to the hydrogen-bonded OH stretching vibrations in the complex PhOH...(H2O)4 (4A). The complexation leads to very large red shifts of these vibrations and very strong increase in their IR intensity. The predicted red shifts for these vibrations with B3LYP/6-31G(d,p) calculations are in very good agreement with the experimentally observed. It was established that the phenolic OH stretching vibration is the most sensitive to the hydrogen bonding. The predicted red-shift with the B3LYP/6-31G(d,p) calculations for the most stable ring structure 4A (-590 cm(-1)) is in better agreement with the experimentally observed than the red-shift, predicted with SCF/6-31G(d,p) calculations. The magnitude of the wavenumber shift is indicative of relatively strong OH...H hydrogen-bonded interaction. The complexation between phenol and four water molecules leads to strong increase of the IR intensity of the phenolic OH stretching vibration (up to 38 times).