FT-IR,FT-Raman,NMR spectra and DFT calculations on 4-chloro-N-methylaniline

In this work, the vibrational spectral analysis was carried out by using FT-IR and FT-Raman spectroscopy in the range 400–4000 and 50–3500 cm^?1 respectively, for the title molecule. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method using 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments of all the vibrational mode were performed on the basis of the total energy distributions (TED). ¹³C and ¹H NMR chemical shifts results were given and are in agreement with the corresponding experimental values. The theoretically constructed FT-IR and FT-Raman spectra exactly coincides with experimental one.     

FT-IR and FT-Raman vibrational spectra and molecular structure investigation of nicotinamide: A combined experimental and theoretical study

In this work, the experimental and theoretical spectra of nicotinamide (C₆H₆N₂O) are studied. FT-IR and FT-Raman spectra of title molecule in the liquid phase have been recorded in the region 4000–100 cm^?1. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree–Fock and density functional method (B3LYP) with the 6-31+G*(d, p) and 6-31++G* (d, p)basis set. The vibrational frequencies have been calculated and scaled values have been compared with the experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found in good agreement. The DFT-B3LYP/6-31++G (d, p) calculations have been found are more reliable than the ab initio HF/6-31+G (d, p) calculations for the vibrational study of nicotinamide. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands due to the substitutions in the base molecule is also investigated from their characteristic region of linked spectrum.     

Vibrational study of caffeic acid phenethyl ester,a potential anticancer agent,by infrared,Raman, and NMR spectroscopy

The structural and vibrational properties of caffeic acid phenethyl ester (CAPE) were studied using infrared and Raman spectroscopy in the solid phase and multidimensional nuclear magnetic resonance (NMR) spectroscopy in solution. The theoretical structures of the compound and of its dimer in the gas phase and in DMSO solution by using density functional theory (DFT) were studied. The harmonic vibrational frequencies for the optimized geometry of CAPE and its dimeric species were calculated at the B3LYP level of theory using the 6–31G* basis set. These data allow a complete assignment of the vibration modes of the FTIR and Raman spectra in the solid state using the scaled quantum mechanical force field (SQMFF) methodology. The vibrational analysis for the dimer was performed taking into account the correlation diagram by means of the factor group analysis in accordance with the experimental structure determined by X-ray diffraction. The presence of the dimer of CAPE is supported by the IR bands at 1654, 1635, 1563, 1533, 1300, 1107, 1050, 738 cm⁻¹ and the Raman bands at 1684, 1681, 1634, 1112, 1050, 928, 873, 850, 740, 445, 371 and 141 cm⁻¹. The calculated ¹H and ¹³C chemicals shifts are consistent with the corresponding experimental NMR spectra of the compound in solution. In addition, a natural bond orbital (NBO) study revealed the characteristics of the electronic delocalization of the stable structure, while the corresponding topological properties of the electronic charge density were analyzed by employing Bader's atoms in the molecules theory (AIM).     

Vibrational and electronic properties of single-walled and double-walled boron nitride nanotubes

We calculated IR, nonresonance Raman spectra and vertical electronic transitions of the zigzag single-walled and double-walled boron nitride nanotubes ((0,n)-SWBNNTs and (0,n)@(0,2n)-DWBNNTs). In the low frequency range below 600 cm⁻¹, the calculated Raman spectra of the nanotubes showed that RBMs (radial breathing modes) are strongly diameter-dependent, and in addition the RBMs of the DWBNNTs are blue-shifted reference to their corresponding one in the Raman spectra of the isolated (0,n)-SWBNNTs. In the high frequency range above ∼1200 cm⁻¹, two proximate Raman features with symmetries of the A_1g (∼1355 ± 10 cm⁻¹) and E_2g (∼1330 ± 25 cm⁻¹) first increase in frequency then approach a constant value of ∼1365 and ∼1356 cm⁻¹, respectively, with increasing tubes’ diameter, which is in excellent agreement with experimental observations. The calculated IR spectra exhibited IR features in the range of 1200–1550 cm⁻¹ and in mid-frequency region are consistent with experiments. The calculated dipole allowed singlet–singlet and triplet–triplet electronic transitions suggesting a charge transfer process between the outer- and inner-shells of the DWBNNTs as well as, upon irradiation, the possibility of a system that can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides the photochemical and other photophysical processes.     

Electronic absorption,vibrational spectra,non-linear optical properties,NBO analysis and thermodynamic properties of 9-[(2-hydroxyethoxy) methyl] guanine molecule by density functional method

The Fourier transform infrared (FT-IR) and FT-Raman of 9-[(2-hydroxyethoxy) methyl] guanine (9-2HEMG) have been recorded in the regions 4000–100 and 4000–400 cm⁻¹, respectively. A complete assignment and analysis of the fundamental vibrational modes of the molecule were carried out. The observed fundamental modes have been compared with the harmonic vibrational frequencies computed using DFT (B3LYP) method by employing 6-31G(d,p) and 3-21G basis sets. The vibrational studies were interpreted in terms of potential energy distribution. The first order hyperpolarizability (β₀) and related properties (α, μ and Δα) of this molecular system are calculated using B3LYP/6-31G(d,p) method based on the finite-field approach. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the σ* and π* antibonding orbitals and second-order delocalization energies (E(²⁾) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV–vis spectrum of the compound has been recorded and electronic properties such as excitation energies, oscillator strength and wavelength are calculated by TD-DFT and CIS methods using B3LYP/6-31G (d,p) basis set. Molecular electrostatic potential (MEP) and HOMO–LUMO energy levels are also constructed. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (C_p,m), standard entropies (S_m) and standard enthalpy changes (H_m) increase with rise in temperature.     

Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

The experimental and DFT studies of 1,3-dimethyl-2-[4-chloro-styryl]-benzimidazolium iodide

1,3-Dimethyl-2-[4-chloro-styryl]-benzimidazolium iodide (1) was synthesized and characterized by X-ray diffraction, ¹H NMR, MS, IR, UV–vis spectra and elemental analysis. The crystals are monoclinic, space group P2₁/c, with a = 12.507(3) Å, b = 7.3259(19) Å, c = 36.705(9) Å, V = 3358.9(15) Å³, and Z = 4 (at 296(2) K). Crystal stacking scheme indicates the face-to-face π?π aromatic stacking interactions. Molecular geometries, frequencies, IR, ¹H NMR and UV–vis were calculated at DFT/TD-DFT level using two hybrid exchange–correlation functionals, B3LYP and PBE1PBE. The stability of the molecule arising from hyperconjugative interaction and charge delocalization had been analyzed using natural bond orbital (NBO) analysis. These calculations on (1) provide deep insight into its electronic structure and properties.     

Raman study of natural berlinite from a geological phosphate deposit

Natural berlinite from a heated sedimentary sequence in Cioclovina Cave (Romania) was studied using Raman spectroscopy complemented with infrared techniques. Vibrational data acquired at room temperature were compared with those reported for synthetic berlinite in ambient conditions. The symmetry of the (PO₄)^3? units is confirmed by the observation of characteristic bands attributed to the ν₁(PO₄)^3? stretching mode, both the ν₄ and ν₂ bending regions at 500–595 cm^?1, and 350–500 cm^?1, respectively. The berlinite Raman fingerprint was unambiguously identified at 1111 and 1104 cm^?1, confirming the identity of the species and elucidating some controversial reports in the mineralogy field.The vibrational data of natural berlinite relates to its crystallography, and along with the spectra–structure correlation, confirmed an almost ideal natural berlinite crystal.     

Ab initio studies of molecular structures,conformers and vibrational spectra of heterocyclic organics: I. Nicotinamide and its N-oxide

FTIR spectra of nicotinamide and its N-oxide have been recorded and analyzed in the range 400–4000 cm^?1. The stabilities, optimized molecular geometries, APT charges and vibrational characteristics for the two possible conformers of nicotinamide and its N-oxide have been studied theoretically using restricted Hartree–Fock (RHF) and density functional theory (DFT) methods. The E (trans) conformers of nicotinamide and its N-oxide are found to be more stable and less polar than their respective Z (cis) conformers. Due to addition of an O atom at the N₁ site in the NA molecule the magnitudes of atomic charges on all the H atomic sites are found to increase. For all the studied molecules, magnitude of the wagging mode of the NH₂ group is found to be higher than its torsion mode, which is in the reverse order as compared to that for the aniline molecule. Most of the vibrational frequencies have nearly the same magnitude for the two conformers of nicotinamide and its N-oxide, however, significant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands. The frequency of the ring breathing mode for the NA molecule is found to decrease by 100 cm^?1 in going to the NANO molecule for both the conformers. The IR intensity for the scissoring mode of the CON(H₂) group is found to decrease significantly for the NA-II conformer as compared to that for the NA-I conformer.     

Trimethylsilyl trichloroacetate vibrational,structural and electronic properties and their comparison with related acetates

The molecular structure of trimethylsilyl trichloroacetate, CCl₃C(O)OSi(CH₃)₃, was determined by ab initio (MP2) and DFT calculations using 6-31G(d), 6-311G(d,p), 6-311++G(d,p) and 6-311++G(3df,3pd) basis sets. The infrared and Raman spectra for the liquid phase were also recorded and the bands observed assigned to the vibrational normal modes. The study was completed using natural bond orbital (NBO) analysis and atoms in molecules (AIM) calculations. The comparison between the calculated molecular geometrical parameters, conformation and vibrational properties and those measured for CX₃C(O)OR [X = F, Cl and R = CH₃, Si(CH₃)₃] was of particular interest in order to check the behavior of the CO and CO with respect to the different substitutions. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to estimate the measured wavenumbers with a final root-mean-square deviation of 8.92 cm⁻¹.     

Spectroscopic investigation of the interaction of p-benzoquinone with casein in the solid state

The reaction between p-benzoquinone (PBQ) and casein (protein) in the solid state was studied. After reaction with protein, the FT-IR spectra showed a new band at 1215 cm^?1, with an intense sign attributed for casein/PBQ product. An optimum amount of PBQ for determination of the product when mixed with casein was 100 mg and a reaction time of 30 min. The product was stable for a period of 24 h after the reacting by heating. The interaction of PBQ with casein was investigated by FT-IR, reflectance, Raman and EPR spectroscopies. The reaction between PBQ and casein in the solid state yields a radical species (p-benzosemiquinone) that it is stabilized by the presence of p-biphenolate and p-benzoquinone species in the solid state.     

DFT and Raman spectroscopy of porphyrin derivatives: Tetraphenylporphine (TPP)

Raman spectrum of the meso tetraphenylporphine (TPP) deposited onto smooth copper surface as thin film were recorded in the region 200–1700 cm⁻¹. To investigate the effect of meso-phenyl substitution rings on the vibrational spectrum of free base porphyrin, we calculated Raman and infrared (IR) spectra of the meso-tetraphenylporphine (TPP), meso tetramethylporphine (TMP), copper (II)porphine (CuPr) and free base porphine (FBP) at the B3LYP/6-311+G(d,p) level of the density functional theory (DFT). The observed Raman spectrum of the TPP is assigned based on the calculated its Raman spectrum in connection with the calculated spectra of the TMP, CuPr and FBP by taking into account of their corresponding vibrational motions of the Raman modes of frequencies. Results of the calculations clearly indicated that the meso tetraphenyl substitution rings are totally responsible for the observed Raman bands at ∼1593, 1234 and 1002 cm⁻¹. The calculated and observed Raman spectra also suggested that the observed Raman band with a medium intense at 962 cm⁻¹ might result from the surface plasmon effect. Furthermore, the observed Raman bands with medium intense at ∼334 and ∼201 cm⁻¹ are as results of the dimerization or aggregation of the TPP or would be that related to intramolecular interaction. We also calculated IR spectra of these molecules at same level of the theory. To investigate the solvent effect on the vibrational spectrum of porphine, the Raman and IR spectra of the TPP and FBP are calculated in solution phase where water used as solvent. The results of these calculation indicated that there is no any significant effect on the vibrational spectrum of the TPP.     

Spectroscopic investigations and structural confirmation studies on thiourea

The Fourier transform infrared and Raman spectra of thiourea have been studied in the region 4000–400 and 4000–10 cm^?1, respectively. A complete vibrational analysis on the molecular structure of thiourea has been made on the basis of C_2υ point group symmetry. The validity of the vibrational assignments on the structure of thiourea is supported by evaluating the molecular constants and the potential energy distribution.     

Vibrational spectroscopic study of brazilin and brazilein,the main constituents of brazilwood from Brazil

In this work, the vibrational spectra (FT-Raman and infrared spectra) of brazilin, the major component of brazilwood Caesalpinia echinata (from Bahia, Brazil), and brazilein, the oxidised pigment, are investigated. The FT-Raman spectra of the compounds show different patterns in the carbonyl stretching region, where brazilein presents a Raman feature at 1697 cm⁻¹ that is tentatively assigned to a coupled vibrational mode described by CO and aromatic CC stretching. Infrared measurements are used to support this assignment. The spectral region between 1700 and 1500 cm⁻¹ is also proposed as a fingerprint for brazilin and brazilein. Comparisons with some quinones and polyalcohols as parent molecules and other deep red resin pigments such as “dragon’s blood” are undertaken to assist the vibrational assignment. As a test of the spectroscopic protocol for the identification of these pigments in natural brazilwoods, an 80-year-old archival specimen of Caesalpinia echinata was analysed non-destructively and the feature of brazilein shown from the Raman spectrum.     

Temperature dependent Raman study of SB → SC transition in liquid crystalline compound N-(4-n-pentyloxybenzylidene)-4′-heptylaniline (5O.7)

Temperature dependent Raman study of C–H in-plane bending mode (～1163 cm^?1 and ～1190 cm^?1) and C–C stretching mode of phenyl ring (～1571 cm^?1 and ～1594 cm^?1) of N-(4-n-pentyloxybenzylidene)-4′-heptylaniline (5O.7) has been done. Vibrational assignment and potential energy distribution (PED) of individual modes have been calculated employing density functional theory (DFT) for the first time. The S_B → S_C transition is nicely depicted in the variation of the linewidth of the ～1163 cm^?1 band and the peak position of ～1594 cm^?1 band with temperature. Because of a small amount of charge density transfer from the core part to the alkyl chain region, the ～1163 cm^?1 band shifts towards lower wavenumber side whereas the ～1190 cm^?1 band towards higher wavenumber side at S_B → S_C transition. The ～1571 cm^?1 and ～1594 cm^?1 bands are assigned as 8a and 8b modes, whose relative intensity variation with temperature gives the evidence of increased possibility of C–H bending motion of the linking group and the C–C stretching of the alkyl chain in S_C phase.     

Near-infrared spectroscopy: A powerful tool in studies of acid-treated clay minerals

The benefit of near-infrared (NIR) spectroscopy in studies of acid-treated clay minerals is demonstrated. The effects of mineral type, composition and content of non-swelling interlayers on the dissolution rate are investigated. Detailed analysis of the NIR region is performed by comparing the first overtone (2ν_OH) and combination (ν + δ)_OH bands with the fundamental stretching (ν) and bending (ν) vibrations. Spectra of acid-treated samples show a gradual decrease in the intensities of the structural OH overtone (near 7100 cm^?1) and combination (4600–4300 cm^?1) bands reflecting a fewer number of octahedral atoms. The appearance of the 2ν_SiOH vibration for terminal (isolated) SiOH groups near 7315 cm^?1 indicates the formation of a protonated silica phase. The band near 7130 cm^?1 remaining in the spectra of acid-treated samples is assigned to 2ν_HOSiOH of geminal silanol groups. Thus the creation of geminal silanols, previously detected by ²⁹Si MAS-NMR spectroscopy in acid-treated hectorite, is confirmed also by NIR spectroscopy. The assignment of the 4555 cm^?1 band to the (ν + δ)_SiOH combination enabled calculation of the wavenumber for the SiO–H bending vibration (～810 cm^?1) that is not observable in the mid-IR region due to overlapping with the Si–O band of amorphous silica (～800 cm^?1). The NIR spectra confirm that trioctahedral hectorite is much more susceptible to dissolution in HCl than dioctahedral nontronite. The dissolution rate of kaolinite present in the Badin clay as an admixture is lower than that of the main mineral nontronite. The accessibility of the interlayers for protons significantly influences the stability of clay minerals in HCl. Mixed-layered mineral illite/smectite with only 30% of swelling interlayers dissolves more slowly than smectite of similar chemical composition containing mainly swelling interlayers.     

Synthesis and photovoltaic properties of organic sensitizers containing electron-deficient and electron-rich fused thiophene for dye-sensitized solar cells

Diverse fused thiophenes with electron-rich and electron-deficient blocks have been synthesized and employed as the π-conjugated spacers of organic dyes for the dye-sensitized solar cells (DSSCs). The effects of these fused thiophenes were investigated by their absorption spectra, electrochemical and photovoltaic properties. For a typical device a maximum power conversion efficiency of 6.11% was obtained under simulated AM 1.5 irradiation (100 mW cm^?2): a short-circuit current (J_SC) of 14.47 mA cm^?2, an open-circuit voltage (V_OC) of 670 mV, and a fill factor (FF) of 0.63.     

Molecular and vibrational structure of the extracellular bacterial signal compound N-butyryl-homoserine lactone (C4-HSL)

The molecular and vibrational structure of the title compound (C4-HSL) was studied by experimental and theoretical methods. The infrared (IR) absorption spectrum was measured in the solid state and in CCl₄ suspension. The observed absorption bands were compared with transitions obtained with B3LYP/cc-pVTZ density functional theory (DFT) calculations. Two stable molecular conformations were predicted, corresponding to an endo- and an exo-conformer with similar energies. Intermolecular amide–amide hydrogen bonding in the crystal state was approximated by a simple cluster model, leading to excellent agreement with the observed solid state IR spectrum. Due to the low solubility of C4-HSL in common solvents for IR spectroscopy, such as CS₂ and CCl₄, a liquid solution spectrum of pure, monomeric C4-HSL was not obtained. However, absorbance peaks observed in oversaturated CCl₄ solution could be assigned to distinct contributions from suspended micro-crystalline aggregates and dissolved monomeric species. The key vibrational bands of the monomeric form of C4-HSL are reported here for the first time: 3425 cm^?1 [ν(N–H)], 1784 cm^?1 [ν(CO), lactone], 1688 cm^?1 [amide I], and 1494 cm^?1 [amide II] (CCl₄).     

Spectroscopic characterization of Cu(II) complex of l-phenylalanine and d,l-tryptophan

In this work, the reactions involving l-phenylalanine and d,l-tryptophan in the presence of Cu(II) ion were studied. Optimum conditions for the reactions were established as pH 7 and λ = 641 nm. When the reaction was kinetic, it was observed that the following rate formula was found as dA/Aⁿ = k dt and k = 3.2 × 10^?4 s^?1, according to absorbance measurements. Using a perpetual change curve, the ratio of [Cu]/[Cu] + l-phenylalanine + [d,l-tryptophan] was found 1:1:1. According to this result, one molecule of l-phenylalanine and one molecule of d,l-tryptophan react with one molecule Cu(II) ion.