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NMR, FT-IR, Raman and UV-Vis spectroscopic investigation and DFT study of 6-Bromo-3-Pyridinyl Boronic Acid
Abstract
Possible stable conformers and geometrical molecular structures of 6-Bromo-3-Pyridinyl Boronic acid (6B3PBA; C5H5BBrNO2) were studied experimentally and theoretically using FT-IR and Raman spectroscopic methods. FT-IR and Raman spectra were recorded in the region of 4000–400 cm−1 and 3700–400 cm−1, respectively. The structural properties were investigated further, using 1H, 13C, 1H coupled 13C, HETCOR, COSY and APT NMR techniques. The optimized geometric structures were searched by Becke-3–Lee–Yang–Parr (B3LYP) hybrid density functional theory method with 6-311++G(d, p) basis set. Vibrational wavenumbers of 6B3PBA were calculated whereby B3LYP density functional methods including 6-311++G(d, p), 6-311G(d, p), 6-311G(d), 6-31G(d, p) and 6-31G(d) basis sets. The comparison of the experimentally and theoretically obtained results using mean absolute error and experimental versus calculated correlation coefficients for the vibrational wavenumbers indicates that B3LYP method with 6-311++G(d, p) gives more satisfactory results for predicting vibrational wavenumbers when compared to the 6-311G(d, p), 6-311G(d), 6-31G(d, p) and 6-31G(d) basis sets. However, this method and none of the mentioned methods here seem suitable for the calculations of OH stretching modes, most likely because increasing unharmonicity in the high wave number region and possible intra and inter molecular interactions at OH edges lead some deviations between experimental and theoretical results. Moreover, reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated using scaled quantum mechanical (SQM) method.
... The green syntheses of TTCPE molecules optimized by visualize using GaussView 5.0 software as displayed in Fig. 2. Geometry optimized properties of bond distance and bond angle interpreted B3LYP/6-311++G (d, p) technique as seen in Table 2 [24,25]. These bond parameters provide useful information on a chemical compound's stability and its effectiveness of the bonds of molecules that keep its atoms connected. ...
... The vibrational assignment on CMIO compound using to calculated by nonlinear formula 3N-6=[(3×33)− 6]=93, that exhibit of 33 atoms and 93 normal modes of vibration. Commonly, the vibrational modes are described by Gauss view 05 software and Potential Energy Distribution (PED) outcome by VEDA 04 [33]. The present study of vibrational in each normal mode done by theoretical method which has efficient tool for fundamental analysis of molecules and the FT-IR spectra observed intensity and wave numbers as shown in Fig. 3. ...
In the current study, the CMIO molecules synthesised from carbinol crude of the Hybanthus Enneaspermus plant
was identified in GC–MS results. The vibrational frequencies assigned through theoretical and experimental
results are well correlated. The electronic transitions n→π*, n→σ* performed by the TD-DFT approach. The
optimized geometry structure found stability for single bonds (S1–C15), double bonds (C19––
C21) and was
compared with XRD values. Donor-acceptor interaction and highest bond strength investigated by the NBO
population. Energy gap, electrophilicity, nucleophilicity index, Mulliken population analysis, MEP plot analysis
of reactive sites, and all the theoretical parameters interpreted by the B3LYP/6–311G(d,p) technique. Moreover,
the various degree-based topological indices used to analyse the CMIO molecules and the docking studies show
excellent binding energy between ligand and 2RFN protein against kidney cancer activity.
... On the other hand, since the energy difference between the conformational states of these molecules is quite low, these molecules might contain more than one conformational state in solid form. In this case, it is difficult to characterize such molecules [9][10][11][12][13][14][15]. Phenylboronic acid and its derivatives have been used in organic synthesis, biosensors and nanoparticular systems. ...
4-Carboxy Phenylboronic acid (4-cpba) was investigated theoretically and experimentally by spectroscopic methods such as FT-IR and Raman. The molecular structure and spectroscopic parameters were determined by computational methods. The molecular dimer1, dimer2 and trimer structures were investigated for intermolecular hydrogen bonding. Moreover, minimum conformational energy search was carried out by potantial energy surface (PES). Potential energy distribution analysis of normal modes was performed to identify characteristic frequencies. The findings of this research work should be useful to experimentalists in their quests for functionalised 4-cpba derivatives.
... CC stretching vibrations of the aromatic ring are very crucial because they determine characteristic of the aromatic ring. In the literature, CC stretching vibrations are observed between 1620 and 1320 cm -1 in the FT-IR spectrum [35]. The experimental and computed IR and Raman spectra of 6A2T5CA are given in Figures 2 and 3. CC stretching vibrations of the title molecule were observed at 1578 cm -1 and 1418 cm -1 in the FT-IR spectrum. ...
Molecular structure, tautomeric forms, vibrational modes, optic and electronic properties of 6-Aza-2-thiouracil-5-carboxylic acid (6A2T5CA) molecule were characterized by FT-IR, Raman, UV-VIS spectral methods and DFT method. The experimental results Show that FT-IR and Raman spectroscopic methods could be used to determine the different tautomeric forms of 6A2T5CA molecule clearly. Although title molecule has different tautomeric forms such as oxo and hydroxy because of inter molecular interactions, it has other tautomeric forms, as well due to intra molecular interaction of functional groups within the molecule. In particular, such structures change between each other depending on the solvent. Differences in some vibrational bands were observed in IR and Raman spectra of the molecule which were dissolved in ethanol and water and the solid form. These differences were observed especially in N-H and O-H functional groups. In addition, vibrational modes, optimized structures, energy values, electronic transitions and HOMO-LUMO energy values of tautomeric forms were calculated using B32LYP/6-311G(2d,2p) level of theory. Experimentally obtained results were compared with theoretically obtained results and it was indicated that there was a good agreement between each other. It was also observed that the molecule has a different tautomeric form when it was dissolved in ethanol, however the molecule has another tautomeric form when it was dissolved in water.
... Phenylboronic acid and its derivatives and serine have been characterized by various spectroscopic and theoretical methods [7][8][9][10][11][12][13][14]. Much more effective and important molecules can reveal by bonding serine molecule with boronic acid derivative molecules. ...
(4-boronobenzoyl)serine (4BBS) was synthesized and investigated theoretically and experimentally by spectroscopic methods such as FT-IR, Raman and NMR. The molecular structure, spectroscopic parameters and geometric parameters were determined by computational methods. All theoretical calculations were carried out using B3LYP method and 6-311++G(d,p) basis set. Total energy distribution analysis of normal modes was performed to identify characteristic frequencies. To investigate structure of title molecule using NMR, ¹H, ¹³C, ¹³C APT, ¹H-¹⁷O and ¹H-¹⁵N HMQC, ¹H-¹³C HMBC, ¹H-¹³C HETCOR, ¹H-¹H NOESY and ¹H-¹H COSY NMR experiment were performed. These results should be useful for the experts in their studies based on functionalized phenylboronic acid derivatives.
... 4-cpba (C 7 H 7 BO 4 ) is a phenylboronic acid derivative. Phenylboronic acid and its derivatives have been characterized by various spectroscopic and theoretical methods [4][5][6][7][8][9][10]. They have been generally used in organic synthesis, nanoparticle science engineering, preparation of sugar sensitive electrodes. ...
Solvent dependent structural properties of 4-carboxy phenylboronic acid (4-cpba) were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopic methods. The molecular structure and geometric parameters were determined by some computational methods such as B3LYP/6-31 + G(3df,p), HF/aug-cc-pvtz and MP2/6-31G(d). Detailed elucidation of the structural and spectroscopic properties of 4-cpba was carried out with ¹H, HETCOR and DOSY NMR experiments. Solvent effects on the structural properties were monitored on the changes of ¹H NMR spectra by using various solvents and it was observed that 4-cpba shows serious structural preferences depending on the solvent used.
Carbohydrate sensing in an aqueous solution remains a very challenging area of interest. Using the idea of covalent reversible interaction between boronic acids and the diol groups in carbohydrates enable us to design a carbohydrate sensor 1-thianthrenylboronic acid (1T), which has high selectivity towards fructose. To elucidate the sensing and binding properties of 1T with sugars, we have incorporated theoretical (DFT and TD-DFT) and spectroscopic techniques. For an optimized geometry, the complete vibrational assignments were done with FT-IR and FT-Raman spectra. Physiochemical parameters were obtained by implementing frontier molecular orbital (FMO) analysis. Further, excited state properties were determined by performing TD-DFT calculations in solvent and these properties were in good agreement with the experiment. The steady state fluorescence measurements with varying concentration of sugars, revealed that the fluorescence intensity of boronic acid is enhanced by studied sugars due to the structural modification. We also noticed remarkable changes in fluorescence lifetimes and quantum yield after adding sugars. The article also reports influence of pH on boronic acid’s fluorescence intensity with and without sugars. The fluorescence of boronic acid increases with the increase in pH. These changes are due to acid–base equilibrium of boronic acid and led us to estimate the pKa value of 7.6. All the theoretical and experimental evidences suggested that 1T can be used as a possible fluorescent sensor for fructose. In addition, 1T showed very good affinity for Cu2+ ion with Ka = 150 × 102 M−1, which suggests that 1T can also be used as a chemosensor for Cu2+ ions.
A new palladium(II) complex, [Pd(PPh3)(4-NO2-BZH)Cl2], bearing 4-Nitrobenzhydrazide and triphenylphosphine ligands has been synthesized and mainly characterized with single crystal X-ray diffraction analysis, FT-IR, Raman and NMR spectroscopic methods. Theoretical calculations were performed to explain chemical structure and vibrational properties. The geometric optimization, vibrational wavenumbers and chemical shift values of the title compound were investigated using the DFT/ B3LYP method, 6-311G++(d,p) and LanL2DZ level of theory. An agreement between the experimental and the theoretical results was observed. The high chemical reactivity of the title compound was theoretically examined by calculating the chemical potential, electrophilicity index, chemical hardness and global electrophilicity index.
A nickel (II) compound, [Ni(C6H5CH2COO)(C12H8N2)2](ClO4)(CH3OH), bearing phenyl acetic acid (paa) and 1,10′-phenanthroline (phen) ligands was synthesized and characterized using single crystal X-ray diffraction (XRD), FT-IR, Raman and UV-VIS spectroscopic methods. This compound belongs to triclinic system with space group P-1. In order to explain chemical structure and vibrational properties, theoretical calculations were performed. All theoretical computations were carried out using the DFT method at B3LYP/LanL2DZ level of theory. We obtained good agreement between the experimental and the theoretical results. Using the DFT method, HOMO-LUMO energies values were computed to get an insight into the material. Detailed information about local and global chemical activity, electrophilic and nucleophilic nature of complex were theoretically obtained. Moreover, UV-VIS spectrophotometer and fluorescence spectrophotometer were used to determine the interaction between complex and CT-DNA. Obtained results indicate that there are strong chemical interaction between CT-DNA and complex. Complex shows electrostatic or groove mode binding with CT-DNA. This complex can destroy the DNA acting on cancer cells. In order to develop anti-cancer drugs, It is hoped that this study may help theoretically and experimentally to produce anticancer drugs.
Polyoxymethylene dimethyl ethers (H3CO(CH2O)nCH3, PODEn or DMMn,n ≥ 2) with unique physical and chemical properties are a potential additive for diesel fuels, which can effectively enhance the combustion efficiency and reduce the emission of pollutants. In this work, a series of pure PODEn components (n = 2–5) were synthesized from methylal and trioxymethylene and obtained with high purity through collaborative separation; their structure and properties were characterized by NMR, FT-IR, Raman, DSC and DFT calculation and a detailed assignment of the expressions in the spectrogram to the various groups was performed. A detailed assignment of expressions in the spectrogram to the various groups was also performed. The density and viscosity of PODEn were measured at 298.15–323.15 K. The results indicate that the density and viscosity of PODEn decrease gradually with the increase of temperature. Meanwhile, with the increase in the number of –CH2O– units (n) from 2 to 5, the density, viscosity, flash point, pour point, and the heat of fusion and solidification of PODEn are all increased with the increase in the chain length. These results are valuable for the practical synthesis and application of PODEn.
Two boronic acid copolymers were synthesized by free radical polymerization of 3-acrylamidophenylboronic acid/4-vinylphenylboronic acid with N-acryloyl-L-alanine and vinyl acetate to investigate the role of the boronic acids in the fluorescence response mechanism. The structure and the chemical composition of the formed copolymers (COP-1, COP-2) were confirmed by ¹HNMR and FTIR spectroscopy. The UV–vis spectrum profiles of the copolymers are similar, meanwhile their emission spectra (λex = 330 nm) are different: COP-1 has two emission bands (386 nm and 500 nm) and COP-2 emits blue fluorescence with a single maximum in its spectrum (385 nm). Both copolymers were tested as fluorescent sensors at physiological pH for detection of diols, namely sugars (glucose, sucrose) and catecholamines (dopamine), COP-1 showing higher efficiency for such compounds. Also, the sensitivity for dopamine (Cmin = 4 × 10⁻⁵ M) was higher than for the sugar derivatives (Cmin = 6 × 10⁻⁴ M) and the fluorescence quenching of the copolymers mainly occurred through dynamic processes. An enhancement of sensor sensitivity was performed by the in situ photogeneration of gold nanoparticles (Au NPs) in COP-1 solution upon exposure to UV irradiation. The minimal dopamine concentration detected was 4 × 10⁻⁶ M, and the value was lower with an order of magnitude compared to COP-1 alone (4 × 10⁻⁵ M).
Crystals of the title compound, C6F5B(OH)(2), were obtained from an attempted recrystallization of (C6F5)(3)B3O3.Et3PO from THF/hexane solution. The central B atom of the boronic acid has a trigonal planar configuration with two hydroxyl groups and one pentafluorphenyl substituent.
In this work, the experimental and theoretical study on the structures and vibrations of 3,4-dichlorophenylboronic acid (3,4-dcpba, C6H3B(OH)(2)Cl-2) are presented. The Fourier Transform Infrared spectra (4000-400 cm(-1)) and the Fourier Transform Raman spectra (3500-5 cm(-1)) of the title molecule in the solid phase have been recorded. There are four conformers for this molecule. The computational results diagnose the most stable conformer of 3,4-dcpba as the ct form. The geometrical parameters and energies have been obtained for all four conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The vibrations of stable and unstable conformers of 3,4-dcpba are researched with the aid of quantum chemical calculations. 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 molecular structures, vibrational frequencies, Infrared intensities and Raman scattering activities were calculated. The spectroscopic and theoretical results are compared. The optimized bond lengths, bond angles and calculated frequencies showed the excellent agreement with the experimental results. The theoretical spectrogram for the Infrared and Raman spectrum of the title molecule has been constructed.
The molecular structure of the title compound, C6H5BF2O2, is essentially planar (mean deviation = 0.019 angstrom), indicating electronic delocalization between the dihydroxyboryl group and the aromatic ring. In the crystal structure, inversion dimers linked by two O-H center dot center dot center dot O hydrogen bonds arise. An intramolecular O-H center dot center dot center dot F hydrogen bond reinforces the conformation and the same H atom is also involved in an intermolecular O-H center dot center dot center dot F link, leading to molecular sheets in the crystal.
The title compound, 2-(CH(3)CH(2)CH(2)CH(2)O)C(6)H(4)B(OH)(2), exists as a centrosymmetric hydrogen-bonded dimer. Dimers are linked via C-H⋯π and π-π [with closest C⋯C contact of 3.540 (3) Å] inter-actions to produce a two-dimensional array.
Complete (1)H, (13)C, (19)F and (11)B NMR spectral data for 28 potassium organotrifluoroborates are described. The resonance for the carbon bearing the boron atom is described for most of the studied compounds. A modified (11)B NMR pulse sequence was used and better resolution was observed allowing the observation of (11)B-(19)F coupling constants for some of the studied compounds.
2-Bromo-5-pyridylboronic acid 2a, 2-chloro-5-pyridylboronic acid 2b, 2-methoxy-5-pyridylboronic acid 2c, and 5-chloro-2-methoxy-4-pyridylboronic acid 4 have been synthesized and shown to undergo palladium-catalyzed cross-coupling reactions with heteroaryl bromides to yield novel heteroarylpyridine derivatives. The X-ray crystal structures of 2a and 2b have been obtained.
The molecular geometries and harmonic vibrational frequencies of biphenyl in the ground and the first excited triplet states have been calculated using the Hartree-Fock and Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with 6-31G* basis set. Structural change occurs from a twisted benzene-like to a planar quinone-like form upon the excitation to the first excited state. Scaled harmonic vibrational frequencies for the ground state obtained from the B3LYP calculation show good agreement with the available experimental data. A few vibrational fundamentals for both states are newly assigned based on the B3LYP results.
The effects of halogen and solvent on the conformation and carbonyl stretching of 4-chloro-3-halogenobenzaldehydes [C7H4ClXO; X=F (CFB), Cl (CCB) or Br (CBB)] were investigated using the density functional theory (DFT) method. The B3LYP functional was used by the 6-311+G(3df,p) basis set in combination with the polarizable continuum model (PCM). Computations were focused on the cis and trans isomers of the compounds in 18 different polar or non-polar organic solvents. The theoretical frequencies of the solvent-induced CO stretching vibrations were correlated with the empirical solvent parameters such as the Kirkwood-Bauer-Magat (KBM) equation, the solvent acceptor number (AN), Swain parameters and the linear solvation energy relationships (LSER). The present work explores the effect of both the halogen and medium on the conformational preference and CO vibrational frequency. The findings of this work can be useful to those systems involving changes in the conformations analogous to the compounds studied.
Copyright © 2015 Elsevier B.V. All rights reserved.
The complete vibrational assignment and analysis of the fundamental vibrational modes of Trifluoperazine (TFZ) was carried out using the experimental FT-IR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G (d,p) basis set. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. The HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as first hyperpolarizability of TFZ have been computed using B3LYP quantum chemical calculation.
The experimental and theoretical vibrational spectra of 2-fluorophenylboronic acid (2fpba) were studied. The Fourier transform Raman and Fourier transform infrared spectra of the 2fpba molecule were recorded in the solid phase. The structural and spectroscopic analysis of the molecule was carried out by using Hartree-Fock and density functional harmonic calculations. For the title molecule, only one form was found to be the most stable structure, by using B3LYP level with the 6-31++G(d,p) basis set. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution (TED). The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the 2fpba molecule were calculated using the Gauge-Invariant- atomic orbital (GIAO) method in DMSO solution using IEF-PCM model and compared with the experimental data. Finally, geometric parameters, vibrational wavenumbers and chemical shifts were compared with available experimental data of the molecule. Copyright © 2009 John Wiley & Sons, Ltd.
In this study, the Fourier-transform infrared (FT-IR) and FT-Raman spectra of 3,5-dichlorophenylboronicacid (3,5-dcpba) were
recorded in the solid phase. The structural and spectroscopic analysis of the 3,5-dichlorophenylboronic was made by using
density functional harmonic calculations. There are three conformers for thismolecule. The computational results diagnose the
most stable conformer of 3,5-dcpba as the ct form. The geometrical parameters and energies have been obtained for all three
conformers from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The vibrations of stable and unstable conformers of
3,5-dcpba are researched by using quantum chemical calculations. The complete assignments were performed on the basis
of the total energy distribution (TED) of the vibrational modes calculated with the scaled quantum mechanics (SQM) method.
The stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using
the natural bond orbital (NBO) analysis. The results show that the charge in electron density (ED) in the ¥ð
. and ¥ò
. antibonding
orbitals and E2 energies confirms the occurrence of ©¥ntermolecular charge transfer (ICT) within the molecule. Finally, the
calculation results were applied to simulated infrared and Raman spectra of the title compound, which show agreement with
the observed spectra. Copyright�c 2009 JohnWiley & Sons, Ltd.
Infrared and Raman spectra of 1-formylpiperazine (1-fp) have been recorded in the region of 4000-50cm(-1). The conformational analysis, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 1-fp (C5H10N2O) have been examined by means of Becke-3-Lee-Yang-Parr (B3LYP) density functional theory (DFT) method together with 6-31++G(d,p) basis set. Furthermore, reliable conformational investigation and vibrational assignments have been made by the potential energy surface (PES) and potential energy distribution (PED) analyses, respectively. Calculations are carried out with the possible six conformational isomers of 1-fp, both in gas phase and in solution using benzene and methanol. The experimental and theoretical results indicate that B3LYP method provides satisfactory evidence for the prediction vibrational wavenumbers, and the normal chair conformation with equatorial substituents is not preferred due to the steric interaction.
With the specific target of calculating the pKa values of boronic acids (RB(OH)2) in aqueous solution we inquired the solute–solvent interactions of these acids and their corresponding conjugate base. Relative pKa values were computed for each boronic acid using methylboronic acid (CH3B(OH)2) as a reference. All gas phase computations were performed at (MP2/6-311++G(d,p)//B3LYP/6-31+G(d)) level of theory. Solvation was included in the calculations using the polarized continuum model (PCM) at the HF/6-31G(d,p) level. The geometry optimization of studied structures was performed with DFT computation and the optimized structures were used to carry out Natural Bond Orbital (NBO) analysis. Natural Bond Orbital (NBO) analysis was examined as indicator for the variations observed in the calculated pKa. Natural resonance theory (NRT) was used to calculate the natural bond order and predict bond polarity. The NRT results indicate that the O–H bonds in all studied compounds have an electrovalency character. The results revealed that difference in acid strength is more relevant to the type of substituent. The electron withdrawing substituent will increase the acidic strength. However, the electron releasing substituent will have a reverse effect and decrease the acidic strength. There are good agreement between theoretical values and experimental results for this series of compounds, the average error was found to be less than 1.2 pKa unit.
The microwave spectrum of indene, C9H8, has been recorded from 18.0 to 39.0 GHz. Only a-type R branches were observed and assigned. The determined rotational constants are: A = 3775.01 ± 0.13, B = 1580.86 ± 0.01 and C = 1122.24 ± 0.01 MHz. These rotational constants are shown to be consistent with previously proposed structural parameters for this molecule. The quantity Ia + Ib − Ic = 3.231 U·Å2 is shown to arise from the two out-of-plane hydrogen atoms and the heavy atom skeleton is, therefore, shown to be planar.
In this work, the vibrational characteristics of 4-(trifluoromethyl) benzylbromide (TFMBB) have been investigated and both the experimental and theoretical vibrational data indicate the presence of functional groups in the title molecule. The density functional theoretical (DFT) computations were performed at the B3LYP/6-311+G (d,p) levels to derive the optimized geometry, vibrational wavenumbers with IR and Raman intensities. Furthermore, the molecular orbital calculations such as natural bond orbitals (NBOs), HOMO-LUMO energy gap and Mapped molecular electrostatic potential (MEP) surfaces were also performed with the same level of DFT. The thermal flexibility of molecule in associated with vibrational temperature was also illustrated on the basis of correlation graphs. The detailed interpretation of the vibrational spectra has been carried out with the aid of potential energy distribution (PED) results obtained from MOLVIB program. The delocalization of electron density of various constituents of the molecule has been discussed with the aid of NBO analysis.
The L-shaped method is useful for solving two-stage stochastic linear programming problems which have the form of a master problem and several subproblems represented by the side model. In order to make this approach possible, the random vector ξ, which is bringing the uncertainty into the model, must have finite support. With finite support we may write the deterministic equivalent program in the extensive form which is solvable by decomposition. To avoid the problems arising from the random elements that have continuous probability distributions, an approximate discretisation is needed. In this paper, the uniform continuous probability distributions of the yields in the Farmer's problem are discretised by using one of the low-discrepancy sequences, called Faure sequence, and based on the obtained approximate discrete distribution a heuristic is proposed to approximate the solution to the problem.
Possible stable forms and molecular structures of 2,6-dimethoxyphenylboronic acid (2,6-dmpba) were studied experimentally and theoretically using FT-IR, Raman, liquid–solid state NMR and XRD spectroscopic methods. FT-IR and Raman spectra were recorded in the region of 4000–200cm−1. 13C cross-polarization magic-angle spinning NMR and liquid phase 1H, 13C and HETCOR NMR spectra of 2,6-dmpba ((CH3O)2C6H3B(OH)2) were reported. The optimized geometric structures concerning to the minimum on the potential energy surface was investigated by Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional theory method together with 6-31++G(d,p) basis set. Vibrational wavenumbers and 1H, 13C NMR chemical shifts of 2,6-dmpba were calculated by means of B3LYP density functional methods with 6-31++G(d,p) basis set. Comparison between the experimental and theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting vibrational wavenumbers and nuclear magnetic shielding tensors. Furthermore, reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method.
FT-IR and Raman spectra together with the vibrational spectral assignments between 4000 and 400cm−1 of 4-(1-Pyrrolidinyl)piperidine (4-pypp) have been reported. The optimized structural parameters (bond lengths, bond and dihedral angles), normal mode frequencies and corresponding vibrational assignments of 4-pypp (C9H18N2) have been theoretically examined by means of B3LYP density functional method with 6-31G(d) basis set. Infrared intensity and Raman activities have also been calculated and reported. Theoretical results have been successfully compared against obtained experimental data.
We wish to present an experimental and theoretical study for the estimation of pKa values of some 1-, 2- and 1,2-substituted indoles in aqueous solution by spectroscopic and semiempirical methods. The all possible tautomeric equilibria and conformers, if available, of the structures were considered to determine the most stable tautomers and conformers. The calculated pKa values were correlated with those found experimentally.
A new boronic acid protecting group, 1-(4-methoxyphenyl)-2-methylpropane-1,2-diol (MPMP-diol), has been developed. Both protection and deprotection can be accomplished under mild conditions with quantitative conversions. The deprotection can be carried out using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).
This study examined absorption properties of 2-styrylpyridine, trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)]pyridine, and trans-4-(m-cyanostyryl)pyridine compounds based on theoretical UV/Vis spectra, with comparisons between time-dependent density functional theory (TD-DFT) using B3LYP, PBE0, and LC-ωPBE functionals. Basis sets 6-31G(d), 6-31G(d,p), 6-31+G(d,p), and 6-311+G(d,p) were tested to compare molecular orbital energy values, gap energies, and maxima absorption wavelengths. UV/Vis spectra were calculated from fully optimized geometry in B3LYP/6-311+G(d,p) in gas phase and using the IEFPCM model. B3LYP/6-311+G(d,p) provided the most stable form, a planar structure with parameters close to 2-styrylpyridine X-ray data. Isomeric structures were evaluated by full geometry optimization using the same theory level. Similar energetic values were found: ∼4.5 kJ mol(-1) for 2-styrylpyridine and ∼1 kJ mol(-1) for derivative compound isomers. The 2-styrylpyridine isomeric structure differed at the pyridine group N-atom position; structures considered for the other compounds had the cyano group attached to the phenyl ring m-position equivalent. The energy difference was almost negligible between m-cyano-substituted molecules, but high energy barriers existed for cyano-substituted phenyl ring torsion. TD-DFT appeared to be robust and accurate approach. The B3LYP functional with the 6-31G(d) basis set produced the most reliable λ(max) values, with mean errors of 0.5 and 12 nm respect to experimental values, in gas and solution, respectively. The present data describes effects on the λ(max) changes in the UV/Vis absorption spectra of the electron acceptor cyano substituent on the phenyl ring, the electron donor methyl substituent, and the N-atom position on the electron acceptor pyridine ring, causing slight changes respect to the 2-styrylpyridine title compound.
The theory of atoms in molecules (AIM) defines bounded atomic fragments in real space that generate transferable atomic properties. As part of a program that investigates the topological partitioning of electromagnetic properties based on the electron density, we have calculated the exact atomic electrostatic potential (AEP) of an AIM atom in a molecule. Second we expand this atomic electrostatic potential in terms of AIM electrostatic multipole moments based on spherical tensors. We prove that the convergence of this expansion is faster than previously assumed, even for complicated atomic shapes.
Density functional theory (DFT) using the 6-31G* basis set and two nonlocal exchange-correlation functionals (Becke-Lee-Yane-Parr [B-LYP] and the three-parameter compound function of Becke [B3-LYP]) has been used for the calculation of vibrational force fields of a set of 31 organic molecules including a wide range of functional groups. The calculated force constants have been scaled to experimental vibrational frequencies by using (a) an overall scaling constant and (b) a set of 11 factors paying respect to the different kinds of internal coordinates. The comparison of the scaled fundamental frequencies with experiment shows that density functional theory is a reliable tool for the interpretation of IR spectra. The uncorrected DFT frequencies and force constants approximate the experimental ones in a much more uniform fashion than does Hartree-Fock theory. Nevertheless, the use of multiple scale factors leads to further significant improvement. The scaled B3-LYP results are superior to the B-LYP ones, even though the unsealed B-LYP frequencies are, through error cancellation, slightly better than the B3-LYP ones. The reliability of scaled force fields is demonstrated by comparing the calculated and experimental vibrational spectra of aniline.
This work presents the characterization of 2,3-difluorophenylboronic acid (abbreviated as 2,3-DFPBA, C(6)H(3)B(OH)(2)F(2)) by quantum chemical calculations and spectral techniques. The spectroscopic properties were investigated by FT-IR, FT-Raman UV-Vis, (1)H and (13)C nuclear magnetic resonance (NMR) techniques. The FT-IR spectrum (4000-400cm(-1)) and the FT-Raman spectrum (3500-10cm(-1)) in the solid phase were recorded for 2,3-DFPBA. The (1)H and (13)C NMR spectra were recorded in DMSO solution. The UV-Vis absorption spectra of the 2,3-DFPBA that dissolved in water and ethanol were recorded in the range of 200-400nm. There are four possible conformers for this molecule. The computational results diagnose the most stable conformer of the 2,3-DFPBA as the trans-cis form. The structural and spectroscopic data of the molecule were obtained for all four conformers from DFT (B3LYP) with 6-311++G (d,p) basis set calculations. The theoretical wavenumbers were scaled and compared with experimental FT-IR and FT-Raman spectra. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method, interpreted in terms of fundamental modes. We obtained good consistency between experimental and theoretical spectra. (13)C and (1)H NMR chemical shifts of the molecule were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, absorption wavelengths, HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. Finally the calculation results were analyzed to simulate infrared, Raman, NMR and UV spectra of the 2,3-DFPBA which show good agreement with observed spectra.
A general introduction is given to the principles and theory of Raman spectroscopy, the discipline dealing with spectral analysis of inelastic scattering of light by the vibrating molecules in liquids, solids, or gases – the phenomenon called Raman scattering. The origin of Raman scattering and its association with molecular polarizability is outlined in this article. The frequency relations of the vibrational Raman effect are developed in terms of the classical theory of electromagnetic radiation. A simplified description of the factors governing the directional properties, intensity relations, and polarization characteristics of the scattered radiation are given by the classical theory, which are then refined according to a partial quantum mechanical treatment. The vibrational selection rules including the role of molecular symmetry are demonstrated using select examples of diatomic and polyatomic molecules, contrasting infrared and Raman spectroscopy and emphasizing their complementary nature.
The experimental and theoretical vibrational spectra of 4-chloro- and 4-bromophenylboronic acids (abbreviated as 4Clpba and 4Brpba) were studied. The Fourier transform Raman and Fourier transform infrared (FTIR) spectra of 4Clpba and 4Brpba molecules were recorded in the solid phase. The structural and spectroscopic analyses of the molecules were made by using Hartree–Fock and density functional harmonic calculations. In both 4Clpba and 4Brpba only one form was most stable using B3LYP level with the 6–311 + + G(d,p) basis set. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution (TED). Finally, geometric parameters as well as infrared (IR) and Raman bands were compared with the experimental data of the molecules. Copyright © 2008 John Wiley & Sons, Ltd.
The IR (3200–30 cm−1) spectra have been recorded for S-methyl-N,N-dimefhylthiocarbamate, (CH3)2NC(O)SCH3, and its isotopomers, S-d3, N-d6 and N-d9, for the gas and liquid. Additionally, the Raman spectra (3200–10 cm−1) for the solid and liquid, with qualitative depolarization ratios, have been obtained for all the isotopes. These data are interpreted on the basis that the s-cis conformer (the S-methyl group oriented eis to the carbonyl group) with Cs symmetry is the only form existing in all three phases for this molecule. A complete vibrational assignment proposed for the -d0 molecule is facilitated by the availability of spectral data for five different isotopomers. A normal coordinate analysis has been carried out utilizing ab initio calculations with the 3–21G* basis set. The potential energy distributions and ab initio calculated frequencies have allowed a clarification of some of the corresponding results obtained from experiment. Structural optimizations and potential surface scan have also been carried out by ab initio calculations with the 3–21G* basis set. These results are compared with some previous studies on this molecule as well as on similar molecules.
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The solid phase FTIR and FT-Raman spectra of methylboronic acid (MBA) have been recorded in the regions 400-4000 and 50-4000 cm(-1), respectively. The spectra were interpreted interms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (B3LYP) and HF method with 6-311++G(d,p) as basis set. The vibrational frequencies were calculated for most stable conformer 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. (1)H and (13)C NMR spectra were recorded and (1)H and (13)C 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 200-400 nm and the electronic properties HOMO and LUMO energies were calculated by time-dependent TD-DFT approach. Mulliken charges of the MBA molecule was also calculated and interpreted. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman intensities and absorption wavelengths were compared with the available experimental data of the molecule.
Scaling factors for obtaining fundamental vibrational frequencies, low-frequency vibrations, zero-point vibrational energies (ZPVE), and thermal contributions to enthalpy and entropy from harmonic frequencies determined at 19 levels of theory have been derived through a least-squares approach. Semiempirical methods (AM1 and PM3), conventional uncorrelated and correlated ab initio molecular orbital procedures [Hartree?Fock (HF), M?ller?Plesset (MP2), and quadratic configuration interaction including single and double substitutions (QCISD)], and several variants of density functional theory (DFT:? B-LYP, B-P86, B3-LYP, B3-P86, and B3-PW91) have been examined in conjunction with the 3-21G, 6-31G(d), 6-31+G(d), 6-31G(d,p), 6-311G(d,p), and 6-311G(df,p) basis sets. The scaling factors for the theoretical harmonic vibrational frequencies were determined by a comparison with the corresponding experimental fundamentals utilizing a total of 1066 individual vibrations. Scaling factors suitable for low-frequency vibrations were obtained from least-squares fits of inverse frequencies. ZPVE scaling factors were obtained from a comparison of the computed ZPVEs (derived from theoretically determined harmonic vibrational frequencies) with ZPVEs determined from experimental harmonic frequencies and anharmonicity corrections for a set of 39 molecules. Finally, scaling factors for theoretical frequencies that are applicable for the computation of thermal contributions to enthalpy and entropy have been derived. A complete set of recommended scale factors is presented. The most successful procedures overall are B3-PW91/6-31G(d), B3-LYP/6-31G(d), and HF/6-31G(d).
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