The molecular structures, vibrational spectroscopies (FT-IR and Raman) and quantum chemical calculations of n-alkyltrimethylammonium bromides

The FT-IR and micro-Raman spectra of three n-alkyltrimethylammonium bromides (dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and hexadecyl(cetyl)trimethylammonium bromide (CTAB)) in powder form were recorded in the regions 4000–550 cm^?1 and 3200–300 cm^?1, respectively. The optimized geometries and vibrational frequencies of DTAB, TTAB and CTAB have been carried out with ab initio Hartree-Fock (HF) and density functional theory method B3LYP calculations with the 6–31 G (d, p) basis set in the ground state. The comparison of the observed fundamental vibrational frequencies and calculated results for the fundamental vibrational frequencies of DTAB, TTAB and CTAB indicate that the scaled B3LYP method is superior compared to the scaled HF method.     

Molecular structure,NMR and vibrational spectral analysis of 2,4‐difluorophenol by ab initio HF and density functional theory

Quantum chemical calculations of energies, geometries and vibrational wavenumbers of 2,4‐difluorophenol (2,4‐DFP) were carried out by using ab initio HF and density functional theory (DFT/B3LYP) methods with 6‐311G(d,p) as basis set. The optimized geometrical parameters obtained by HF and DFT calculations are in good agreement with related molecules. The best level of theory in order to reproduce the experimental wavenumbers is the B3LYP method with the 6‐311G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of 2,4‐DFP is also reported. The entropy of the title compound was also performed at HF/6‐311G(d,p) and B3LYP/6‐311G(d,p) levels of theory. The isotropic chemical shift computed by ¹H, ¹³C NMR analyses also shows good agreement with experimental observations. The theoretical spectrograms for FT‐IR and FT‐Raman spectra of the title molecule have been constructed. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular structure,vibrational spectroscopic studies and natural bond orbital analysis of 7-amino-4-trifluoromethyl coumarin

Quantum mechanical calculations of energies, geometries and vibrational wave numbers of 7-amino-4-trifluoromethyl coumarin (7A4TFMC) were carried out using Hartree-Fock (HF) and density functional theory (DFT) using hybrid functional BLYP and B3LYP with 6–31G(d,p) as basis set. The optimized geometrical parameters obtained by HF and DFT calculations are in good agreement with the experimental X-ray data. The best method to reproduce the experimental wave numbers is B3LYP method with the 6–31G(d,p) basis set. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the infrared spectra of 7A4TFMC was also reported. The entropy of the title compound was also performed at HF using the hybrid functional BLYP and B3LYP with 6–31 G(d,p) as basis set levels of theory. Natural bond orbital (NBO) analysis of the title molecule is also carried out. The theoretical spectrogram for FTIR spectra of the title molecule has been constructed.     

一种对羟基苯甲醛希夫碱的红外光谱及核磁共振理论研究

采用Gaussian03软件,用密度泛函理论的B3LYP方法在6-31G基组水平上优化了对羟基苯甲醛缩2,4-二硝基苯胺希夫碱,得到其最稳定构型及其能量。在优化结构基础上用Hartree-Fock(HF)/6-31G方法计算了该分子的红外光谱振动频率并绘制了红外光谱图,对图中各峰位进行了分析探讨。用同样的方法计算了该化合物分子的核磁共振氢谱。     

4-氟苯甲醛酪氨酸席夫碱的制备及其振动光谱的密度泛函理论和从头算理论计算的研究

4-氟苯甲醛酪氨酸席夫碱(4-FT)由4-氟苯甲醛和L-酪氨酸钾盐在室温条件下反应制得,4-FT的结构通过1HNMR,FTIR和Raman测试得到确认。分别用密度泛函(DFT,density functional theory)理论的B3LYP(Becke’s three-parameter exchange functional(B3)with Lee,Yang,Parr(LYP))方法和从头算(ab initio)理论的HF(Hartree-Fock)方法,选用标准的6-31G**和6-31G*基组对化合物4-FT的几何构型进行优化。同时分别在B3LYP/6-31G**,B3LYP/6-31G*,HF/6-31G**和HF/6-31G*水平下计算4-FT的振动波数。用密度泛函(DFT)的B3LYP方法计算并校正后的波长数据比用从头算(ab i-nitio)的HF方法计算的结果更与实验数据吻合。     

Conformational stability and vibrational study of phenylacetyl chloride

The Fourier transform infrared spectroscopy and Fourier transform Raman spectra of phenylacetyl chloride were recorded and analyzed in the range 3500–400 and 3500–200 cm^?1 at room temperature, respectively. In order to obtain the structural information and conformational stabilities, a potential energy surface scan for internal rotation was carried out at the B3LYP/6‐31G(d) level. The potential energy surface reveals that the title compound has two minimal conformers (A and B). The optimized geometries, structural parameters, stabilities, energies, thermodynamic parameters, vibrational wavenumbers, infrared intensities, and Raman activities for the two conformers (A and B) have been obtained by employing B3LYP and MP2 calculations with 6‐311++G (d, p) basis sets. The conformational energy difference between A and B is very small, indicating that the B conformer coexists with the A conformer. The detailed vibrational assignments of vibrational spectra of each conformer have been made on the basis of the potential energy distributions analysis. The highest occupied molecular orbital –lowest unoccupied molecular orbital energy gap and molecular electrostatic potential of the two conformers have been also calculated for comparison of their chemical activities. Copyright © 2015 John Wiley & Sons, Ltd.     

Si2CmN团簇的结构及稳定性的密度泛函理论研究

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对Si2CmN(m=2-10)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=2-10的团簇为线性结构,随着m的增大,团簇的自旋多重度均为2,Si原子在C与N原子形成的线性链端部成键,团簇的基态能量近似线性增大。m为偶数的Si2CmN团簇比m为奇数的更为稳定。     

A combined experimental and computational studies of 3,3,6,6-Tetramethyl-9-(4-Methoxyphenyl)3,4,6,7,9,10 hexahydroacridine-1,8-dione

ABSTRACT

In this work, we have recorded the Fourier Transform Infrared (FTIR) and Ultra-Violet Visible (UV–Vis) spectra of 3,3,6,6-Tetramethyl-9-(4-Methoxyphenyl)3,4,6,7,9,10 hexahydroacridine-1,8-dione (C₂₄H₂₉NO₃) in the spectral range 4000–400?cm^?1 and 190–1400?nm, respectively. The thermo gravimetric (TG) analysis of the compound has been performed to check the thermal stability of the compound. The molecular geometry and complete vibrational spectra in the ground state are calculated by Hartree Fock (HF) and Density Functional Theory (DFT) using6-311G(d,p) basis set. The calculated vibrational harmonic frequencies are scaled using a proper scale factor, yielding a good agreement with the experimental data. Stability of the molecule arising from hyperconjugative interactions, charge delocalisation has been studied using natural bond orbital analysis (NBO). Mulliken charges, MEP mapping and temperature dependence on the thermodynamic properties in the optimised ground state have been calculated. UV–Visible spectrum of the molecule was calculated by using TD-DFT approach and the results were compared with the experimental one. We have calculated the several molecular parameters like ionisation potential, electron affinity, global hardness, electron chemical potential, electronegativity and global electrophilicity based on HOMO and LUMO energy values calculated at B3LYP/6-311G(d,p) level of theory. The calculated optimised structural parameters and vibrational wavenumbers are found to be in good agreement with the experimental results.     

Computational studies of the cone and 1,2,3 alternate calix[6]arene bis‐crown‐4 isomers: structures,NMR shifts,atomic charges,and steric compression

The cone and 1,2,3 alternate isomers of calix[6]arene bis‐crown‐4 were investigated computationally. Structural optimizations, energies, bond distances, and Mulliken charges were calculated by the application of the B3LYP/6‐31g(d) method/basis, followed by NMR calculations via both B3LYP/6‐31g(d) and HF/6‐31g(d). Calculations were completed at three different levels of imposed symmetry, and two calculations investigated the chloroform solvent effects. Better NMR results were obtained from HF/6‐31g(d) calculations that did not impose molecular symmetry constraints. Consideration of solvent effects improved ground state energies, but other improvements were minimal and not significant enough to justify the added computational expense of solvent calculations. Overall results are consistent with known experimental assignments and were valuable for assigning previously unknown NMR peaks. Net charges, electrostatic forces, and local dipoles – but not bond lengths – are strongly correlated to spectroscopic manifestations of steric compression. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantum-chemical calculation on 5-phenyl-2-(4-pyridyl)pyrimidine

The molecular geometry and vibrational frequencies of 5-phenyl-2-(4-pyridyl)pyrimidine in the ground state have been calculated by the density functional theory with B3LYP/6-311G(d) as the basis set. The observed frequencies of 5-phenyl-2-(4-pyridyl)pyrimidine and those calculated are nearly the same. The form of the modes for all fundamentals is based on potential energy distribution calculations.     

Theoretical analysis on structural,spectroscopic, and electronic properties of some 2-aminobenzimidazole complexes by using PBE1PBE,B3LYP,and HF methods

The molecular geometry, vibrational frequencies, gauge including atomic orbital (GIAO) ¹H and ¹³C chemical shift values of ABZ-TNB [ABZ-TNB: 2-aminobenzimidazole-trinitrobenzene] and ABZ-PA [ABZ-PA: 2-aminobenzimidazole-picric acid] in the ground state were calculated by using density functionals (B3LYP and PBE1PBE) and Hartree-Fock (HF) methods with the 6–31 ++ G(d,p) basis set. Furthermore, the electronic spectrum of title complexes was calculated with the time dependent DFT levels (TD-PBE1PBE and TD-B3LYP) and HF (TD-HF) method starting from the ground state geometry optimized in the gas phase. A detailed assignment of vibrational spectra was made on the basis of the calculated potential energy distribution (PED). Total static dipole moment (μ), the mean polarizability (〈α〉), the anisotropy of the polarizability (Δα), the mean first-order hyperpolarizability (〈β〉), highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, chemical hardness (η) and electronegativity (χ) of ABZ-TNB and ABZ-PA complexes were also investigated with quantum chemical calculations. Additionally, data obtained from quantum chemical calculations were compared with the experimental ones.     

(AgBr)6结构计算及对计算方法的依赖

利用HF、B3LYP方法分别结合LANL2DZ,CEP-121G赝势基组及3-21G*全电子基组对(AgBr)6的可能异构体进行结构优化。结果显示,HF、B3LYP方法在各基组水平上优化的(AgBr)6基态结构并不完全一致,表明(AgBr)6结构计算对计算方法具依赖性。对优化后能量始终较低的5个结构,进一步采用MP2方法结合上述基组进行高精度的结构优化。确定(AgBr)6基态结构为双三角形环重叠结构,并计算了该结构的红外光谱。     

(AgBr)6结构计算及对计算方法的依赖

利用HF、B3LYP方法分别结合LANL2DZ,CEP-121G赝势基组及3-21G*全电子基组对(AgBr)6的可能异构体进行结构优化。结果显示,HF、B3LYP方法在各基组水平上优化的(AgBr)6基态结构并不完全一致,表明(AgBr)6结构计算对计算方法具依赖性。对优化后能量始终较低的5个结构,进一步采用MP2方法结合上述基组进行高精度的结构优化。确定(AgBr)6基态结构为双三角形环重叠结构,并计算了该结构的红外光谱。     

密度泛函理论研究SiCmN团簇

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。     

密度泛函理论研究SiCmN团簇

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。     

FT‐Raman,FT‐IR spectra and DFT calculations on monomeric and dimeric structures of 5‐fluoro‐ and 5‐chloro‐salicylic acid

The experimental and theoretical study on the structures and vibrations of 5‐fluoro‐salicylic acid and 5‐chloro‐salicylic acid (5‐FSA and 5‐ClSA, C₇H₅FO₃ and C₇H₅ClO₃) is presented. The Fourier transform infrared spectra (4000–400 cm⁻¹) and the Fourier transform Raman spectra (4000–50 cm⁻¹) of the title molecules in the solid phase were recorded. The molecular structures, vibrational wavenumbers, infrared intensities, Raman intensities and Raman scattering activities were calculated for a pair of molecules linked by the intermolecular O H···O hydrogen bond. The geometrical parameters and energies of 5‐FSA and 5ClSA were obtained for all eight conformers/isomers from density functional theory (DFT) (B3LYP) with 6‐311++G(d,p) basis set calculations. The computational results identified the most stable conformer of 5‐FSA and 5‐ClSA as the C1 form. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The spectroscopic and theoretical results were compared with the corresponding properties for 5‐FSA and 5‐ClSA monomers and dimer of C1 conformer. The optimized bond lengths, bond angles and calculated wavenumbers showed the best agreement with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

FT-IR,FT-Raman spectra and quantum mechanical study of piperidine-3-carboxylic acid and its tautomers,isomers

The mid-IR, far-IR, and Raman spectra of piperidine-3-carboxylic acid were measured and interpreted with support of the MP2 and B3LYP/6-311++G(d, p) calculated harmonic vibrational spectra. 10 stable piperidine-3-carboxylic acid tautomers/isomers were found after B3LYP, calculations. The experimental absorption bands of carboxylate (COO^?) group show that the free piperidine-3-carboxylic acid molecule exists in zwitterionic form and the most stable tautomer (NAT-1) can be stabilized by an intramolecular N-H...O hydrogen bond. All vibrational frequencies of NAT-1 assigned in detail with the help of total energy distribution (TED). The experimental vibrational wave numbers were compared with the calculated data.     

3-氨基-2,5-二氯苯甲酸振动光谱的密度泛函研究

为了本质地把握3-氨基-2,5-二氯苯甲酸(3A2,5DBA)的振动光谱和结构间的关系,在HF和B3LYP水平上利用6-311G(d,p)基组对3A2,5DBA进行了结构优化和振动频率的计算,得到了3A2,5DBA的结构信息和全部45个简正振动模式.通过与苯甲酸的结构参数以及相关文献数据的对比,发现B3LYP/6-311G(d,p)方法较HF/6-311G(d,p)方法能给出更加合理的结果.考虑到计算模拟分子和实验测量样品间的差异,对计算所得到的频率进行了合理的标度修正.在B3LYP/6-311G(d,p)方法下,对波数小于800cm-1的振动频率,标度因子取1.001 3,而波数大于800 cm-1的标度因子取0.961 3.借助Gaussian View程序包对所计算得到的振动模式进行了高精度指认,对3A2,5DBA的主要官能团及取代基团进行了振动分析.通过和实验测量的FTIR数据的比对,发现经标度修正后的计算结果和实验测量符合的很好.同时结合相关的文献报道,表明所做的振动指认和振动分析是合理的.     

对巯基苯胺分子构象和拉曼光谱的密度泛函理论研究

本文采用密度泛函方法B3LYP/6-311+G**计算了对巯基苯胺分子(PATP)的平衡结构和振动拉曼光谱。结果表明该分子有两个稳定构象,反式构象能更低。利用振动模分析所得的势能分布我们对该分子振动基频进行了归属,并计算了低能构象的标度振动频率,其结果与实验值相吻合。     

Pt-CO分子1∑+态的π反馈键与拉曼光谱强度的量子化学研究

采用量子化学方法ＨＦ和Ｂ３ＬＹＰ计算了Ｐｔ－ＣＯ的＾１∑＾＋电子基态的电子结构屯Ｐｔ－Ｃ和Ｃ－Ｏ伸缩振动的拉曼光谱性质，计算结果表明ｄ→２π反馈与Ｐｔ－Ｃ和Ｃ－Ｏ伸缩振动的频率相关。拉曼谱强度理论分析表明人射光频率显著影响计算Ｒａｍａｎ光谱强度。