Density functional theory studies on tautomeric stability and infrared and Raman spectra of some purine derivatives

The molecular vibrations of 6-hydroxy-purine (6HP) and 6-amino-purine (6AP) were investigated in polycrystalline sample, at room temperature by Fourier transform infrared (FTIR) and FT-Raman spectroscopy. The spectra of the above compounds have been recorded in the region 4000-50, 3500-100 cm(-1), respectively. They were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory (DFT) using HF/6-31G* and B3LYP/6-311+G** methods and basis set combinations. The results of the calculations were applied to simulated infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The dipole moment and the tautometric stability of purine derivatives were also studied.     

DFT and ab initio quantum chemical studies on p-cyanobenzoic acid

The Fourier transform infrared (FTIR) and FT-Raman spectra of p-cyanobenzoic acid (CBA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with theoretical wavenumbers obtained from ab initio HF and DFT-B3LYP gradient calculations employing 6-31G**, 6-311++G** and cc-pVTZ basis sets for the optimised geometry of the compound. The geometry and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The normal coordinate analysis was also carried out with ab initio force fields utilising Wilson's FG matrix method. The interactions of cyano and carboxylic acid groups with the skeletal vibrational modes were investigated.     

Structural, vibrational and quantum chemical investigations on 5-chloro-2-hydroxybenzamide and 5-chloro-2-hydroxybenzoic acid

The Fourier transform infrared (FTIR) and FT-Raman spectra of 5-chloro-2-hydroxybenzamide (5CBA) and 5-chloro-2-hydroxybenzoic acid (5C2HBA) have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The complete vibrational fundamental modes of the compounds were assigned and analysed using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with the theoretical wavenumbers calculated from ab initio HF and DFT-B3LYP gradient methods employing 6-31G** and 6-311++G** basis sets. The effect of halogen, hydroxyl groups and hydrogen bonding on the characteristic frequencies of the -COOH and -CONH2 group frequencies have been investigated. In 5CBA and 5C2HBA intramolecular hydrogen bond between a hydroxyl group and CO group makes a six membered ring, which causes the O?H interaction onto the resonance of the benzene ring. Comparison of the positions of the ν(OH) bands shows the ν(OH) band of 5CBA is located at considerably higher frequency which confirms a weaker hydrogen bond than in 5C2HBA.     

Synthesis of N-(fluoro phenyl) maleamic acids and N-(fluoro phenyl) maleimides

A series of seven N-(fluoro phenyl) maleamic acids and their N-(fluoro phenyl) maleimides were prepared by the reaction of fluoro phenyl amines ( o-, m-, and p-fluoro, 2.4-, 2.5-difluoro, 2.3.5.6-tetrafluoro and 2.3.4.5.6.-pentafluoro anilines) with maleic anhydride according to substantial modifications made to the reaction conditions used by Searle for the preparation of normal N-aryl maleimides.     

Fourier transform infrared and Raman spectral investigations of 5-aminoindole

Fourier transform infrared (FT-IR) and Raman (FT-Raman) spectra of 5-aminoindole has been recorded and analysed. The FT-IR spectrum of the compound was recorded in a BrukerIFS 66 V spectrometer in the range 4000-400 cm(-1) and the FT-Raman spectrum was also recorded in the same instrument in the region 3500-100 cm(-1). Observed frequencies for normal modes are compared with those calculated form normal co-ordinate analysis. The shift in the frequencies of the fundamental modes with the substituent amino group and the mixing of different normal modes are discussed with the help of potential energy distribution (PED) calculated through normal co-ordinate analysis.     

Density functional theory studies on vibrational and electronic spectra of 2-chloro-6-methoxypyridine

The Fourier transform infrared (FTIR) and FT-Raman spectra of 2-chloro-6-methoxypyridine have been recorded in the range 3700-400 and 3700-100 cm(-1), respectively. The complete vibrational assignment and analysis of the fundamental modes of the compound was carried out using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with the theoretical frequencies computed by DFT gradient calculations (B3LYP method) employing the 6-31G(d,p), cc-pVTZ and/6-311++G(d,p) basis sets for the optimised geometry of the compound. The geometry and normal modes of vibration obtained from the DFT methods are in good agreement with the experimental data. The normal co-ordinate analysis was also carried out using DFT force fields utilising Wilson's FG matrix method. The influence of the substituents bulky chlorine atom and the methoxy group on the spectral characteristics of the compound has been discussed. The electronic spectrum determined by TD-DFT method is compared with the observed electronic spectrum.     

N-[1-(取代苯基)乙基]-2-羟基苯甲酰肼的合成、表征及抑菌活性

依据邻羟基二苯醚及芳香肼类化合物的抗菌特性, 以邻羟苯基为分子核心, 酰肼键为桥基, 设计合成了7种未见报道的N-(取代苯基)乙基-2-羟基苯甲酰肼类化合物. 以水杨酸甲酯为原料, 经肼解反应后与取代苯乙酮缩合, 再与硼氢化钠反应制得目标化合物, 化合物结构经IR, ¹H NMR和元素分析等证实. 抗菌活性测试结果表明, 该类化合物对不同菌株的抑菌活性具有明显的选择性和特异性. 当质量浓度为1×10^-4 g/mL时, 化合物3b和3e对大肠杆菌和白色念珠菌的抑菌率高达100%, 有极强的抑菌活性; 所有化合物对金黄色葡萄球菌的抑菌率均大于70%, 有一定的抑菌活性. 构效关系分析结果表明, 苯基中引入Cl或Br等卤原子能显著增强化合物的抑菌活性, 而引入-NO₂及-CH₃基团则会降低其抑菌活性.     

FT-IR, NIR-FT-Raman and gas phase infrared spectra of 3-aminoacetophenone by density functional theory and ab initio Hartree-Fock calculations

The gas phase infrared spectrum of 3-aminoacetophenone (3AAP) was measured in the range 5000-500cm(-1) and with a resolution of 0.5cm(-1). The Fourier transform Raman (FT-Raman) and Fourier transform infrared (FT-IR) spectra of 3AAP were recorded in the solid phase. Geometry optimizations were done without any constraint and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and density functional theory (DFT) levels invoking 6-311G(2df 2p) basis set and the results are compared with the experimental values. Harmonic-vibrational wavenumber was also calculated for the minimum energy conformer at ab initio and DFT levels using 6-31G(d,p) basis set and the results are compared with related molecules. With the help of specific scaling procedures, the observed vibrational wavenumbers in gas phase, FT-IR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrogram for the FT-IR spectra of the title molecule is also constructed.     

Vibrational spectra and assignments of 5-amino-2-chlorobenzoic acid by ab initio Hartree-Fock and density functional methods

The Fourier transform Raman and Fourier transform infrared spectra of 5-amino-2-chlorobenzoic acid (5A2CBA) were recorded in the solid phase. Geometry opitimizations were done without any constraint and harmonic-vibrational wavenumber and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-311G(d,p) basis set and the results are compared with the experimental values with the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range, the error obtained was in general very low. The appropriate theoretical spectrograms for the FTIR spectra of the title molecule were also constructed.     

FT-Raman and FTIR spectra, assignments and ab initio calculations of 2-aminobenzyl alcohol

The Fourier transform Raman and Fourier transform infrared spectra of 2-aminobenzyl alcohol (2ABA) were recorded in the solid phase. Geometry optimizations were done with out any constraint and harmonic vibrational wave numbers and several thermodynamic parameters were calculated for the minimum energy conformer at ab initio and DFT levels invoking 6-31g** and 6-311+g(2d, p) basis sets and the results were compared with the experimental values. With the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and FT-Raman spectra were analyzed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. The appropriate theoretical spectrograms for the Raman and IR spectra of 2ABA were also constructed.     

Vibrational spectral investigation of four second order nonlinear optical azobenzene-containing materials: a combination of experimental and density functional theoretical (DFT) study

In this work, four-second order nonlinear optical (NLO) azobenzene-containing materials are studied in-depth by using vibrational spectra and density functional theory (DFT). The Fourier transform infrared (FT-IR) spectra and FT-Raman spectra are recorded in the range of 50-4000 and 100-3600cm(-1), respectively. Meanwhile, the DFT computations are performed at B3LYP/6-31G (d, p) level to derive equilibrium geometry, vibrational wavenumbers and intensities, and first hyperpolarizability, and the scaled theoretical wavenumbers are also shown to be in good agreement with experimental data. The calculated results show that these four azobenzene-containing compounds are good materials and the compound with nitro substituent groups possesses a larger first molecular hyperpolarizability (β) value. Moreover, the simultaneous infrared and Raman activation of R1 group and CC stretching suggest that the charge transfer interaction might occur between the R1 group and phenyl ring, and the HOMO-LUMO gap analysis also supports this viewpoint.     

FT-IR, FT-Raman spectra and ab initio HF, DFT vibrational analysis of p-chlorobenzoic acid

The infrared, the Fourier transform infrared and Fourier transform Raman spectra of p-chlorobenzoic acid (p-CBA) has been recorded in the region 4000-600 cm(-1), 4000-400 cm(-1) and 4000-100 cm(-1), respectively. The optimized geometry, frequency and intensity of the vibrational bands of p-CBA were obtained by the ab initio HF and DFT (B3LYP) methods with complete relaxation in the potential energy surface using 6-311+G(d,p) basis set. The harmonic-vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR 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.     

N-(5-邻氯苯基-2-呋喃甲酰氨基)丙氨酰胺衍生物的合成和 生物活性测定

以5-邻氯苯基-2-呋喃甲酰氯和丙氨酸为起始原料, 通过非均相法得到N-(5-邻氯苯基-2-呋喃甲酰氨基)丙氨酸, 再与10种不同取代苯胺反应, 通过N,N’-二环己基碳二亚胺和4-二甲氨基吡啶(DCC/DMAP)偶合法设计合成了10个未见文献报道的N-(5-邻氯苯基-2-呋喃甲酰氨基)丙氨酰胺类衍生物4a～4j. 通过元素分析, 1H NMR, IR 和MS确定化合物的结构, 初步生物活性测试表明标题化合物具有一定的除草活性.     

Harmonic analysis of vibrations of morpholine-4-ylmethylthiourea: a DFT, midinfrared and Raman spectral study

The FTIR and FT-Raman spectra of morpholine-4-ylmethylthiourea (MMTU) were recorded in the region of mid-IR (400-4,000 cm(-1)). Initial geometry generated from the standard geometrical parameters was relaxed without any constraint on the potential energy surface at MP2 and DFT levels adopting the standard 6-31++G and 6-311+G basis set. With the help of two specific scaling procedures the computed harmonic frequencies have been compared with the observed vibrational wave numbers of FTIR and FT-Raman spectra and assigned to different normal modes of the molecule. Most of the vibrational modes have wave numbers in the expected range. The appropriate theoretical spectrograms of the IR spectra of MMTU have been also constructed.     

Density functional theory calculations and vibrational spectra of 3,5-dibromopyridine and 3,5-dichloro-2,4,6-trifluoropyridine

The solid phase mid FTIR and FT-Raman spectra of 3,5-dibromopyridine (3,5-DBP) and 3,5-dichloro-2,4,6-trifluoropyridine (3,5-DCTFP) have been recorded in the regions 4000-400 cm(-1) and 3500-100 cm(-1), respectively. The spectra were interpreted with the help of normal coordinate analysis (NCA) following full structure optimisation and force field calculations based on the density functional theory (DFT) using the standard B3LYP/6-31G( *) method and basis set combination. The results of the calculations are applied to stimulate infrared and Raman spectra of the title compounds which showed excellent agreement with the observed spectra.     

Ab initio, density functional theory and structural studies of 4-amino-2-methylquinoline

The Fourier transform infrared (FTIR) and FT-Raman spectra of 4-amino-2-methylquinoline (AMQ) have been recorded in the range 4000–400 and 4000–100 cm⁻¹, respectively. The experimental vibrational frequency was compared with the wavenumbers obtained theoretically by ab initio HF and DFT–B3LYP gradient calculations employing the standard 6-31G** and high level 6-311++G** basis sets for optimised geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compounds were carried out using the experimental FTIR and FT-Raman data, and quantum mechanical studies. The geometry and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The potential energy distribution of the fundamental modes was calculated with ab initio force fields utilising Wilson's FG matrix method. The NH-π interactions and the influence of amino and methyl groups on the skeletal modes are investigated.     

Density functional theory calculation of vibrational spectroscopy of trans-1,2-bis(4-pyridyl)-ethylene

The molecular geometry and vibrational frequencies of trans-1,2-bis(4-pyridyl)-ethylene (t-BPE) in the ground state were calculated using density functional theory (DFT) methods with 6–31++G(2d,p) basis set. The optimized geometric bond lengths and bond angles are obtained by DFT employing the hybrid of Beckes nonlocal three-parameter exchange and correlation functional and Lee–Yang–Parr correlation functional (B3LYP). Fourier transform Infrared (FTIR), Fourier transform Raman (FT-Raman) and near-infrared surface-enhanced Raman scattering (NIR-SERS) spectra of t-BPE on the silver foil substrate were recorded. All FTIR, FT-Raman and NIR-SERS band were assigned on the basis of the B3LYP/6-31++G(2d,p) method. The vibrational frequencies obtained by DFT(B3LYP) are in good agreement with observed results. Surface selection rules derived from the electromagnetic enhancement model were employed to infer the orientations of t-BPE on the silver foil substrate surface.     

Crystal Structure and Biological Activities of N-(5-(4-Chloro-2-(trifluoromethyl)phenyl)furan-2- carbonyl)-N'-(4,6-dimethylpyrimidin-2-yl)thiourea

The new title compound N-(5-(4-chloro-2-(trifluoromethyl)phenyl)furan-2-carbon-yl)- N?-(4,6-dimethylpyrimidin-2-yl)thiourea (C19H14ClF3N4O2S) has been synthesized, and its crystal structure and biological behaviors were studied. The title compound crystallizes in the monoclinic system, space group P21/c with a = 7.932(5), b = 33.46(2), c = 7.556(5) , β = 98.058(9)°, V = 1986(2) 3, Mr = 454.85, Z = 4, Dc = 1.521 g/cm3, μ = 0.349 mm–1 and F(000) = 928. The structure was solved by direct methods and refined to R = 0.0724 and wR = 0.1429 for 3494 observed reflections (I > 2σ(I)). Intermolecular hydrogen bonds along the b axis together with the continuous π-π interactions construct the three-dimensional architecture of the title compound. The preliminary biological tests show definite herbicidal activity for the title compound.     

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.