Theoretical and experimental study of the structure and vibration spectra of 4,4′-carbonyl-di-morpholine

4,4′-Carbonyl-di-morpholine was synthesized and characterized by X-ray diffraction, the FTIR and NMR spectra. The extended MO calculations using density functional theory (DFT) and self-consistent field molecular orbital Hartree-Fock theory were carried out. The results of the calculations were compared with experimental data. The experimental and calculated results were supported each other. The performance of a hybrid B3LYP density functional was compared with the ab initio restricted Hartree-Fock method. With the basis sets of the 6-311G** quality, the DFT calculated bond lengths, dipole moments and harmonic vibrations were predicted in a very good agreement with available experimental data.     

Vibrational spectroscopic study of pyrrole and its deuterated derivatives: comparison of the quality of the applicability of the DFT/Becke3P86 and the DFT/Becke3LYP functionals

The aim of our work is a reassignment of the vibrational spectra of pyrrole based on high-level quantum-chemical calculations. This is a continuation of our earlier works on one side of pyrrolydine and N-methylpyrrolidine and on the other side of five-membered ring parent molecules with two-ring nitrogens.

Infrared and Raman spectra are reported for the isotopic species of pyrrole, 1-deuteropyrrole and pentadeuteropyrrole.

The molecular structure and the harmonic force field were calculated applying the ab initio density functional theory (DFT) level with both the Becke3P86 and the Becke3LYP functionals with the 6-311G(d,p) basis set. The force fields were fitted to the experimental fundamentals using in both cases eight scale factors. Though some scaled frequencies show larger deviations from the experimental ones, the percentage deviations of the calculated frequencies from the experimental ones are less than 1.0% for pyrrole and less than 1.2% for the deuterated derivatives in the case of both applied functionals.     

Density functional theory calculation and vibrational spectroscopy study of 2-amino-4,6-dimethyl pyrimidine (ADMP)

The solid phase FTIR and FT-Raman spectra of 2-amino-4,6-dimethyl pyrimidine (ADMP) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The structure was investigated by utilizing density functional theory (DFT) calculations with the Becke 3-Lee-Yang-Parr (B3LYP) method employing the 6-31+G and 6-311++G basis sets. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental data. Complete vibrational assignments were made on the basis of normal coordinate analysis (NCA) for the molecule. The infrared and Raman spectra were also predicted from the calculated intensities. The observed and the calculated spectra were found to be in good agreement. The thermodynamic properties like entropies and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structures.     

Infrared and Raman spectra and quantum chemistry calculations for 2,2,2-trifluoroethyl trichloromethanesulfonate, CCl3SO2OCH2CF3

The infrared spectra of CCl3SO2OCH2CF3 were obtained in the gaseous, liquid and solid states and complemented with the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory (DFT) were used to predict the most stable geometry and conformation of the studied molecule. The harmonic vibrational frequencies and force field were also calculated. Comparison with related molecules and with the predicted frequencies was used as the basis for the assignment of the observed spectral features. Subsequently, a scaling of the original force field by means of a least square procedure was made in order to reproduce as well as possible the experimental frequencies, leading to a final root mean square deviation of 10.6 cm(-1).     

FT-IR, FT-Raman, NMR and UV-vis spectra, vibrational assignments and DFT calculations of 4-butyl benzoic acid

The solid phase FTIR and FT-Raman spectra of 4-butyl benzoic acid (4-BBA) have been recorded in the regions 400-4000 and 50-4000cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for monomer and dimer by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. (13)C and (1)H NMR spectra were recorded and (13)C and (1)H nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was recorded in the region 200-400nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities, chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule.     

Accurate theoretical IR and Raman spectrum of Al2O2 and Al2O3 molecules

The accurate harmonic vibration frequencies together with the infrared (IR) and Raman intensities of the most stable conformers of Al₂O₂ and Al₂O₃ molecules have been calculated by the density functional theory (DFT) method with B3LYP exchange–correlation potential and using a set of the augmented correlated consistent basis sets up to quintuple order. The anharmonic vibration frequencies of the non-linear Al₂O₂ molecule have also been calculated. The obtained equilibrium geometrical parameters, harmonic and anharmonic vibration frequencies along with the IR and Raman intensities good converge to their limits with increasing the size of the used basis set. A comparison of the calculated harmonic and anharmonic vibrational frequencies with the available experimental ones points out that the small differences between the calculated harmonic and experimental frequencies can be further substantially reduced when calculations of the anharmonic vibrational frequencies will be available for all types of molecular geometries.     

Vibrational spectra and structure of 5,6-diamino uracil and 5,6-dihydro-5-methyl uracil by density functional theory calculations

The molecular vibrations of 5,6-diamino uracil and 5,6-dihydro-5-methyl uracil were investigated in polycrystalline sample, at room temperature, by FT-IR and FT-Raman spectroscopies. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculations based on the density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** methods and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compounds. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.     

Vibrational spectra, ab initio calculations, and ring-puckering potential energy function for gamma-crotonolactone

The infrared and Raman spectra of liquid and vapor gamma-crotonolactone have been collected. Both the experimental data and ab initio calculations show that the molecule is rigidly planar in its electronic ground state. This conclusion agrees with the previously reported microwave studies and is attributed to the conjugation between the C=C and C=O double bonds of the ring. The ring-puckering potential energy function was generated from ab initio calculations and was confirmed by the vapor-phase Raman spectra to be nearly harmonic. Density functional theory (DFT) calculations predict a harmonic ring-puckering frequency of 203 cm(-1) as compared to the observed vapor-phase Raman value of 208 cm(-1). The DFT calculations were also used to compute the infrared and Raman spectra of gamma-crotonolactone, and these agree very well with the experimental spectra.     

Density functional theory study on molecular structure and vibrational IR spectra of isocytosine

Density functional theory with the combined Becke3-LYP exchange-correlation energy functional [DFT(B3-LYP) method] using the 6-31G(d, p) basis set is applied to predict molecular parameters (geometries, rotational constants, dipole moments) and vibrational IR spectra (harmonic wavenumbers, absolute intensities) of six tautomers of the isocytosine molecule. The results are compared with the corresponding data calculated at the conventional ab initio Hartree-Fock (HF) level using the same basis set and with available experimental data. Calculations show that (a) three amino tautomers are slightly nonplanar species with, evidently, a distorted amino group, (b) the DFT (B3-LYP)/6-31G(d, p) method predicts better molecular parameters, than do the HF calculations, and (c) the DFT(B3-LYP)-calculated vibrational IR spectra of isocytosine agree well with the available recorded IR spectra, and they show marked improvement over the IR spectra predicted at the HF/6-31G(d, p) level. Tautomeric stabilities of isocytosine are discussed on the basis of computed electronic energies by the DFT(B3-LYP) and ab initio approaches [including the MP2 and MP4(SDQ) calculations of electronic energies] and predicted zero-point vibrational energies by DFT(B3-LYP) and HF methods. This relative energies at 0 K of the tautomeric forms of isocytosine predicted by both conventional ab initio and DFT(B3-LYP) methods correlate well with the experimental data, showing the predominance of the aminohydroxy tautomer of isocytosine for an isolated molecule. © 1997 John Wiley & Sons, Inc.     

黄曲霉素B_2分子吸附在银团簇的表面增强拉曼散射机理

采用密度泛函理论(DFT)B3LYP方法,6-311G(d,p)(C,H,O)/LANL2DZ(Ag)基组,计算了黄曲霉素B2(AFB2)分子吸附在Ag2团簇的表面增强拉曼散射(SERS)光谱和预共振拉曼光谱,并与实验结果比较.结果显示:AFB2分子在基态Ag2团簇表面吸附时,增强因子最大达到102,对应吡喃(pyrane)环C=O伸缩振动,主要是由AFB2分子周围化学环境改变而引起的基态静极化率改变导致的化学增强.不同激发波长下的AFB2分子预共振拉曼光谱的增强强度不同:电荷转移态激发波长为1144和544 nm时拉曼信号增强了102倍,而选择电荷转移预共振波长432和410 nm作为入射光时,其拉曼信号增强了104倍,增强机理为银团簇和黄曲霉素分子之间的电荷转移共振增强.因此通过改变入射光波长,选择电荷转移共振激发波长,更有利于强致癌物AFB2分子的痕量检测.     

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).     

Molecular structure and vibrational raman and infrared spectra of bromochlorofluoromethane and its silicon and germanium analogs: quantum-mechanical DFT and MP2 calculations

DFT(B3LYP) and MP2 calculations with the 6-311G(2d, 2p)-type basis set have been carried out for the prediction of molecular parameters (bond distances, bond angles, rotational constants, and dipole moments) and vibrational Raman and infrared spectra (harmonic wavenumbers, absolute intensities, Raman scattering activities, and depolarization ratios) of bromochlorofluoromethane (HCBrCIF) and its silicon and germanium analogs (HSiBrClF and HGeBrCIF). The predicted geometry and vibrational Raman and infrared spectra of HCBrClF agree well with the available experimental data for this molecule and their deuterated derivatives. This agreement allows one to believe that the predicted molecular parameters and vibrational spectra of HSiBrClF, HGeBrClF, and their deuterated derivatives will guide their future experimental studies.     

Molecular structure and vibrational spectra of γ-oxo [1,1′-biphenyl]-4-butanoic acid (fenbufen) and its interaction with ofloxacin

The Fourier transform Raman and Fourier transform infrared spectra of fenbufen (γ-oxo [1,1′-biphenyl]-4-butanoic acid) were recorded in the solid phase. The gas-phase structure and conformational properties of fenbufen were determined by quantum-chemical calculations (HF and DFT/B3LYP with 6-311++G(d,p) basis set). The harmonic wave numbers were calculated by the density functional theory (DFT) calculations with B3LYP functional and 6-311++G(d,p) basis set, and the scaled values were in good agreement with the majority of the experimental observations. A complete assignment of the fundamentals was proposed based on the total energy distribution (TED) calculation. The possible interaction between fenbufen and ofloxacin which is a synthetic antimicrobial agent was investigated. The changes observed in some bands of mixed drug indicated that there is an interaction between the two drug molecules.     

烷烃客体分子(C_nH_m,n≤6,m≤14)在5~(12)6~2和5~(12)6~4水笼中的稳定性与拉曼光谱的密度泛函理论计算

可燃冰矿藏中气体成分非常复杂,通过谱学分析对水合物样品成分进行指认具有重要意义.基于B97-D/6-311++G(2d,2p)的密度泛函理论(DFT)计算,我们系统地探索了构成水合物的两种标准水笼(51262和51264)包络十八种不同烷烃客体分子的稳定性.从计算结果可以看出,除了3-甲基戊烷和2,3-二甲基丁烷两个烷烃客体分子,其它16个烷烃客体分子都可以被容纳在51262笼中;但是与51262笼不同,十八种烷烃客体分子都可以被容纳在尺寸较大的51264笼中.同时,我们也模拟了五种直链烷烃和四种环状烷烃在51262和51264笼中相应的谱学特征,从拉曼谱图上可以看出,随着碳原子数量的增多,直链烷烃客体分子C―H键伸缩振动区的多数拉曼谱带向高波数移动,而环状烷烃客体分子C―H键伸缩振动区的拉曼谱带则向低波数移动.这些结果为实验上通过拉曼谱测量指认水合物矿藏的成分提供理论参考.     

Fourier transform infrared and Raman spectra, vibrational assignment and density functional theory calculations of naphthazarin

FT Raman and FTIR spectra of Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) and its deuterated analogue are recorded. Comparison between the spectra obtained by two techniques, a series of density functional theory (DFT) calculations and the spectral behavior upon deuteration were used for the assignment of the vibrational spectra of this compound. The calculated vibrational frequencies by the B3LYP, B3PW91, G96LYP, G96P86, and MPWLYP density functionals are generally consistent with the observed spectra. Infrared and Raman vibrational transitions predicted by B3LYP/6-311++G** are reported for the titled compound and its deuterated analogous and the assignments are discussed. All experimental and theoretical results support a relatively weak hydrogen bond in naphthazarin (NZ), compared with that in the enol form of normal beta-diketones. The observed nuOH/nuOD and gammaOH/gammaOD appear at about 3060/2220 and 790/560 cm(-1), respectively, which are consistent with the calculated hydrogen bond geometry and proton chemical shift results. Two bands at about 350 and 290 cm(-1) are assigned to the O...O stretching modes belong to A1 and B2 species, respectively.     

Vibrational spectra and potential energy distributions for 4,5-dichloro-3-hydroxypyridazine by density functional theory and normal coordinate calculations

The solid phase FT-IR and FT-Raman spectra of 4,5-dichloro-3-hydroxypyridazine have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The spectra were interpreted with the aid of normal coordinate analysis following a full structure optimization and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6-31G* and B3LYP/6-311+G** method and basis set combinations. The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. The IR and Raman spectra were predicted theoretically and compared with the experimental spectra.     

Experimental and theoretical investigation of the molecular and electronic structure of anticancer drug camptothecin

The Fourier Transform Infrared spectrum of (S)-4 ethyl-4-hydroxy-1H-pyrano [3',4':6,7]-indolizino-[1,2-b-quinoline-3,14-(4H,12H)-dione] [camptothecin] was recorded in the region 4000-400 cm(-1). The Fourier Transform Raman spectrum of camptothecin (CPT) was also recorded in the region 3500-50 cm(-1). Quantum chemical calculations of geometrical structural parameters and vibrational frequencies of CPT were carried out by MP2/6-31G(d,p) and density functional theory DFT/B3LYP/6-311++G(d,p) methods. The assignment of each normal mode has been made using the observed and calculated frequencies, their IR and Raman intensities. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR and FT-Raman spectra. Most of the computed frequencies were found to be in good agreement with the experimental observations. The isotropic chemical shifts computed by (13)C and (1)H NMR analysis also show good agreement with experimental observations. Comparison of calculated spectra with the experimental spectra provides important information about the ability of computational method to describe the vibrational modes of large sized organic molecule.     

Structures and vibrational frequencies of 2-hydroxy-3-methoxy-5-nitrobenzaldehyde and 2-methoxy-1-naphthaldehyde based on density functional theory calculations

FT-IR and FT-Raman spectra of 2-hydroxy-3-methoxy-5-nitrobenzaldehyde (HMN) and 2-methoxy-1-naphthaldehyde (MN) have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The molecular structure, conformational stability, geometry optimization, vibrational frequencies have been investigated. The total energy calculations of HMN and MN were tried for various possible conformers. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using B3LYP/6-31G* and B3LYP/6-311+G** level and basis set combinations and was scaled using various scale factors yielding good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.     

Ab initio calculation of the vibrational and electronic spectra of trans- and cis-azobenzene

We report accurate geometries and harmonic force fields for trans- and cis-azobenzene determined by second-order M?ller-Plesset perturbation theory. For the trans isomer, the planar structure with C(2h) symmetry, found in a recent gas electron diffraction experiment, is verified. The calculated vibrational spectra are compared with experimental data and density functional calculations. Important vibrational frequencies are localized and discussed. For both isomers, we report UV spectra calculated using the second-order approximate coupled-cluster singles-and-doubles model CC2 with accurate basis sets. Vertical excitation energies and oscillator strengths have been determined for the lowest singlet n(pi)* and (pi)(pi)* transitions. The results are compared with the available experimental data and second-order polarization propagator (SOPPA) and density functional (DFT) calculations. For both isomers, the CC2 results for the excitation energies into the S(1) and S(2) states agree within 0.1 eV with experimental gas-phase measurements.