Structure and vibrational frequencies of 2-butanimine

The conformational behavior and structural stability of 2-butanimine were investigated by utilizing ab initio calculations with 6-311++G** basis set at HF, MP2, B3LYP and BLYP levels. The vibrational frequencies of 2-butanimine were computed. Complete vibrational assignments were made on the basis of normal coordinate calculations for stable conformer of the molecule. HF results without scaled quantum mechanical (SQM) force field procedure considered are in bad agreement with experimental values. Of the two DFT methods, BLYP reproduces the observed fundamental frequencies most satisfactorily with the mean absolute deviation of the non-CH stretching modes less than 21.3 cm(-1). The results indicate that BLYP calculation is a very promising approach for understanding the observed spectral features.     

丙酮酸分子结构与振动光谱的密度泛函理论研究

用密度泛函方法BLYP、B3LYP和从头算Hartree-Fock(HF)方法在6-31G*基组水平上对丙酮酸分子的几何结构（甲基的重叠式和交错式两种构象）和振动光谱分别进行了优化和计算,并给出了各种频率所对应的红外强度及拉曼活性,对光谱进行了指认。结果表明：在丙酮酸分子的两种构象中,重叠式比较稳定*B3LYP计算得到的构型参数与实验结果比较一致;在振动频率的计算中,BLYP未标度力场所计算的非CH3伸缩振动基频预测值和实验值的平均绝对偏差为10.4cm-1;而HF标度力场的平均绝对偏差为17.9cm-1。说明两者的结果与实验观测频率比较吻合,但B3LYP的频率计算值偏差（38.3cm-1）较大。根据振动频率的势能分布和红外光谱强度对此分子的振动基频进行了理论归属。     

Tert-butyl N-(2-bromocyclohex-2-enyl)-N-(2-furylmethyl)carbamate的结构和振动光谱

The molecular structure, conformafional stability, and vibrational frequencies of ten-butyl N-（2- bromocyclohex-2-enyl）-N-（2-furylmethyl）carbamate （TBBFC） were investigated by utilizing the Hartree-Fock （HF） and density functional theory （DFT） ab initio calculations with 6-31G ^＊ and 6-31G^＊ ＊ basis sets. The optimized bond length and angle values obtained by HF method showed the best agreement with the experimental values. Comparison of the observed and calculated fundamental vibrational frequencies indicated that B3LYP was superior to the scaled HF approach for molecular problems. Optimal uniform scaling factors calculated for the title compound are 0.899/0.904, 0.958/0.961, and 0.988/0.989 for HF, B3LYP, and BLYP （6-31G ^＊/6-31G ^＊ ＊）, respectively.     

Theoretical determinations of ionization potentials of dopamine

Adiabatic and vertical ionization potentials (IPs) of nine conformers of dopamine in the gas phase are determined using density functional theory (DFT) B3LYP, B3P86, B3PW91 methods and high level ab initio HF method with 6-311++G** basis set, respectively. And the nine stable cationic states have been found in the ionization process of dopamine. Vertical ionization potentials of nine conformers of dopamine are calculated using the older outer-valence Green’s function (OVGF) calculations at 6-311++G** basis set. Vibrational frequencies and infrared spectrum intensities of G1b and G1b⁺ at B3LYP/6-311++G** level are discussed.     

去氢抗坏血酸分子振动光谱的理论研究

采用RHF, MP2, DFT(B3LYP)方法, 以6-311++G**为基组研究了去氢抗坏血酸分子(DHA)的平衡几何构型和振动光谱. 计算结果表明, 采用RHF, B3LYP以及MP2 方法优化得到的几何结构以及频率值是一致的. 采用B3LYP/6-311++G**计算了DHA分子平衡构型下的谐振动力场﹑振动频率和振动强度. 使用Wilson的GF矩阵方法对DHA分子进行了简正坐标分析, 依据所得的势能分布对DHA分子的振动基频进行了合理的理论归属.     

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 spectrum and assignments of 2-(4-methoxyphenyl)-1H-benzo[d]imidazole by ab initio Hartree-Fock and density functional methods

The room temperature attenuated total reflection Fourier transform infrared spectrum of the 2-(4-methoxyphenyl)-1H-benzo[d]imidazole has been recorded with diamond/ZnSe prism. The conformational behaviour, structural stability of optimized geometry, frequency and intensity of the vibrational bands of the title compound were investigated by utilizing ab initio calculations with 6-311G** basis set at HF, B3LYP, BLYP, B3PW91 and mPW1PW91 levels. The harmonic vibrational frequencies were calculated and scaled values have been compared with experimental IR spectrum. The observed and the calculated frequencies are found to be in good agreement. The theoretical vibrational spectra of the title compound were interpreted by means of potential energy distributions using VEDA 4 program. Furthermore, the optimal uniform scaling factors calculated for the title compound are 0.9120, 0.9596, 0.9660, 0.9699, and 0.9993 for HF, mPW1PW91, B3PW91, B3LYP and BLYP methods, respectively.     

Theory Study on Structures and Vibrational Frequencies of Pyruvic acid

Anumberoftheoreticalstudiesexistforpyruvicacid.IthasbeenstudiedatthesemiempiricalINDOandAMIlevell'2.AttheahinitiolevelstudiesofpyruvicacidrangefromthecalculationofenergiesattheSTO-3Glevel'tocalculationsofenergiesusingtheHF/3-2iG',HF/4-21G',HF/6-3iG*andMP2/4-21Gmethods.ExceptforthestudyofMurtoetal.,allthestudieshavefocussedontheenergiesandgeometriesofpyruvicacid.Moreoveralltheexistingtheoreticalstudieshavefocusedtheirattentionontheorientationofthecarboxylhydrogenextensively.Theorienta…     

Ab initio studies of aspartic acid conformers in gas phase and in solution

Systematic and extensive conformational searches of aspartic acid in gas phase and in solution have been performed. For the gaseous aspartic acid, a total of 1296 trial canonical structures and 216 trial zwitterionic structures were generated by allowing for all combinations of internal single-bond rotamers. All the trial structures were optimized at the B3LYP/6-311G* level and then subjected to further optimization at the B3LYP/6-311++G** level. A total of 139 canonical conformers were found, but no stable zwitterionic structure was found. The rotational constants, dipole moments, zero-point vibrational energies, harmonic frequencies, and vertical ionization energies of the canonical conformers were determined. Single-point energies were also calculated at the MP2/6-311++G** and CCSD/6-311++G** levels. The equilibrium distributions of the gaseous conformers at various temperatures were calculated. The proton affinity and gas phase basicity were calculated and the results are in excellent agreement with the experiments. The conformations in the solution were studied with different solvation models. The 216 trial zwitterionic structures were first optimized at the B3LYP/6-311G* level using the Onsager self-consistent reaction field model (SCRF) and then optimized at the B3LYP/6-311++G** level using the conductorlike polarized continuum model (CPCM) SCRF theory. A total of 22 zwitterions conformers were found. The gaseous canonical conformers were combined with the CPCM model and optimized at the B3LYP/6-311++G** level. The solvated zwitterionic and canonical structures were further examined by the discrete/SCRF model with one and two water molecules. The incremental solvation of the canonical and zwitterionic structures with up to six water molecules in gas phase was systematically examined. The studies show that combining aspartic acid with at least six water molecules in the gas phase or two water molecules and a SCRF solution model is required to provide qualitatively correct results in the solution.     

Molecular structures and vibrational frequencies of 2-, 3- and 4-pyridine carboxaldehydes by ab initio Hartree-Fock and density functional theory calculations

The optimised molecular structures, vibrational frequencies and corresponding vibrational assignments of the cis and trans conformers of 2-, 3- and 4-pyridine carboxaldehydes have been calculated using ab initio Hartree-Fock (HF) and density functional theory (B3LYP) methods with 6-311++G(d, p) basis set. The calculations were adapted to the C(S) symmetries of all the molecules. The mean vibrational deviations between the vibrational frequency values of the two conformers of all the compounds have been seen to increase while the relative energies increase and it was concluded the more different the molecular structure of the two conformers is the higher the relative energy is between them, and thus a bigger mean vibrational deviation.     

Theoretical study on infrared vibrational spectra of boric-acid in gas-phase using density functional methods

Density functional theory (DFT) methods with various exchange-correlation functionals such as SVWN, BVWN, BVWN5, BLYP, B1LYP, B3LYP, B3PW91, and BH and H are employed in a theoretical study of molecular boric-acid in gas-phase. In the calculations, the split valence 6-311++G** and 6-31G* basis sets were used. The geometry, zero-point vibrational energies (ZPVEs), and harmonic infrared vibrational (IR) frequencies are predicted. The calculated C_3h-symmetry geometrical parameters are compared with Hartree–Fock (HF) calculation results and experimental data. IR frequencies predicted by the BLYP, B3LYP, and B3PW91 calculations are in good agreement with experimental data. The frequency calculations presented here also suggest that the C_3h-symmetrical structure corresponds to a minimum in the potential energy surface, but neither is D_3h- or C₃-symmetrical structure.     

FT-IR and NMR investigation of 1-phenylpiperazine: a combined experimental and theoretical study

FT-IR and (1)H, (13)C, DEPT, COSY, NOESY, HETCOR, INADEQUATE NMR spectra of 1-phenylpiperazine (pp) have been reported for the first time except for its (1)H NMR spectrum. The vibrational frequencies and (1)H, (13)C NMR chemical shifts of pp (C(10)H(14)N(2)) have been calculated by means of the Hartree-Fock (HF) and Becke-Lee-Yang-Parr (BLYP) or Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with 6-31G(d) and 6-31G(d,p) basis sets, respectively. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is superior to the scaled HF and BLYP approach for predicting vibrational frequencies and NMR properties.     

Si~2Cl~6分子的内旋转能垒和振动基频的理论研究

用从头算方法HF/6-31G^*^*和密度函方法B3LYP/6-31G^*^*,对Si~2Cl~6分子的平衡几何构型进行优化,优化的结果与实验结果吻合得较好.并用上述两种不同的方法计算Si~2Cl~6分子的内旋转能垒,结果分别为8.786和6.694kJ/mol,其中DFT方法的计算结果与实验结果4.18kJ/mol吻合得较好.对Si~2Cl~6分子的振动基频进行计算.用HF/6-31G^*^*SQM力场所计算的频率理论值与实验值的平均误差为7.3cm^-^1,用B3LYP/6-31G^*^*未标度的力场所计算的频率理论值与实验值的平均误差为6.0cm^-^1.该密度泛函方法(B3LYP/~6-31G^*^*)的理论计算值比用HF/6-31G^*^*标度后的SQM力场计算的频率与实验值(除Si--Si键扭转振动基频之外的11条振动基频)吻合得更好.并给出了Si--Si键扭转振动基频的预测值。     

FT-IR and NMR investigation of 2-(1-cyclohexenyl)ethylamine: a combined experimental and theoretical study

FT-IR and (1)H, (13)C, DEPT, HETCOR, COSY, and NOESY NMR spectra of 2-(1-cyclohexenyl)ethylamine (CyHEA) have been reported for the first time. The vibrational frequencies and (1)H, (13)C NMR chemical shifts of CyHEA (C(8)H(15)N) have been calculated by means of the Hartree-Fock (HF), Becke-Lee-Yang-Parr (BLYP) and Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with 6-31 G(d) and 6-31 G(d,p) basis sets, respectively. The comparison between the experimental and the theoretical results indicates that density functional B3LYP method is superior to the scaled HF and BLYP approach for vibrational frequencies and predicting NMR properties.     

Density functional theory study of vibrational spectra of acridine and phenazine

Density functional theory (DFT) calculations using Becke's exchange in conjunction with Lee-Yang-Parr's correlation functionals (BLYP), Becke's three-parameter hybrid DFT/HF method using Lee-Yang-Parr's correlation functionals (B3LYP) and ab initio Hartree-Fock (HF) method have been carried out to investigate the structure and vibrational spectra of acridine and phenazine. Structural parameters obtained by B3LYP/6-31G* geometry optimization are in good agreement with available experimental data. The raw BLYP non-CH stretching frequencies approximate the experimental results much better than the HF results with the mean absolute deviation about 16 cm(-1). The scaled B3LYP frequencies are more reliable than that of the BLYP and HF methods with the mean absolute deviation about 17 cm(-1). On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes are examined. Also the structure and vibrational frequencies are compared with those of anthracene, pyridine and benzene to study the similarities and differences.     

Combined experimental and theoretical studies on the vibrational spectra of 2-quinolinecarboxaldehyde

Combined experimental and theoretical studies have been performed on the structure and vibrational spectra (IR and Raman spectra including far region) of 2-quinolinecarboxaldehyde. Hartree-Fock (HF) and density functional B3LYP calculations have been employed with the 6-311++G(d,p) basis set for investigating the structural and spectroscopic properties of two possible aldehyde rotamers of 2-quinolinecarboxaldehyde. When the O atom of the aldehyde is farther away than the nitrogen atom of the quinoline, 2-quinolinecarboxaldehyde has the lowest possible energy, and thus is in its ground state. The computed vibrational frequencies of this lowest energy rotamer agree also slightly better than those of the higher energy rotamer with the experimental frequencies after the computed frequencies are scaled.     

FT-IR and FT-Raman investigation, computed vibrational intensity analysis and computed vibrational frequency analysis on m-Xylol using ab-initio HF and DFT calculations

The FT-IR and FT-Raman spectra of m-Xylol molecule have been recorded using Bruker IFS 66V spectrometer in the range 4000-100cm(-1). The molecular geometry and vibrational frequencies in the ground state are evaluated using the Hartree-fock (HF) and B3LYP with 6-31+G (d, p), 6-31++G (d, p) and 6-311++G (d, p) basis sets. The computed frequencies are scaled using a suitable scale factors to yield good agreement with the observed values. The HF and DFT analysis agree well with experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and B3LYP methods indicate that B3LYP/6-311++G (d, p) is superior to HF/6-31+G (d, p) for molecular vibrational problems. The complete data of this title compound provide some useful information for the study of substituted benzenes. The influences of Methyl groups on the geometry of benzene and its normal modes of vibrations have also been discussed.     

FT-IR and FT-Raman spectra and vibrational investigation of 4-chloro-2-fluoro toluene using ab initio HF and DFT (B3LYP/B3PW91) calculations

FT-IR (4000-100 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectra of solid sample of 4-chloro-2-fluoro toluene (4Cl2FT) have been recorded using Bruker IFS 66 V spectrometer. Ab initio-HF (HF/6-311++G (d, p)) and DFT (B3LYP/6-311++G and B3PW91/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. The isotropic HF and DFT analyses showed good agreement with experimental observations. The differences between the observed and scaled wave number values of most of the fundamentals are very small in B3LYP than HF. Comparison of the simulated spectra provides important information about the ability of the computational method (B3LYP) to describe the vibrational modes. The influences of substitutions on the geometry of molecule and its normal modes of vibrations have also been discussed. The changes made by substitutions on the benzene are much responsible for the non-linearity of the molecule. This is an attractive entity for the future studies of non-linear optics.     

Ab initio studies of the conformers and conformational distribution of the gaseous hydroxyamino acid threonine

Systematic and extensive conformational search has been performed to characterize the gas-phase threonine structures. A total of 1296 unique trial structures were generated by allowing for all combinations of internal single-bond rotamers. All the trial structures were optimized at the B3LYP/6-311G* level of the theory and then subjected to further optimization at the B3LYP/6-311++G** level. A total of 71 conformers were found and their rotational constants, dipole moments, zero-point vibrational energies, harmonic frequencies and vertical ionization energies of all the conformers were determined. Single-point energies were also calculated at the MP2/6-311G(2df,p) and B3LYP/6-311G(2df,p) levels. Characteristic H-bonding types were classified and listed for all the conformers. The conformational distributions of gaseous threonine at various temperatures were calculated.     

FT-Raman and FT-IR spectra, ab initio and density functional studies of 3,4-dichlorobenzyl alcohol

The Fourier transform Raman and Fourier transform infrared spectra of 3,4-dichlorobenzyl alcohol were recorded in the solid phase. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, depolarization ratios, reduced masses were calculated by HF and density functional B3LYP method with the 6-311 G** basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The thermodynamic functions of the title compound were also performed at HF/6-311G** and B3LYP/6-311G** levels of theory. A detailed interpretations of the infrared and Raman spectra of 3,4-dichlorobenzyl alcohol is reported. The theoretical spectrograms for FT-IR spectra of the title molecule have been constructed.