Density functional theory study of the rotational barriers,conformational preference,and vibrational spectra of 2-formylfuran and 3-formylfuran

The torsional potentials, molecular structures, conformational stability, and vibrational wavenumbers for the rotational isomers of 2-formylfuran and 3-formylfuran are computed using the density functional theory (B3LYP) method with the 6-31+G* basis set. All structures are fully optimized and the optimized geometries, rotational constants, dipole moments, and energies are presented. From the computations, both 2-formylfuran and 3-formylfuran are predicted to exist predominantly in trans conformation with a cis–trans rotational barrier of 11.19 kcal/mol and 8.10 kcal/mol, respectively. The vibrational wavenumbers and the corresponding vibrational assignments of the molecules in the C _s symmetry are examined and the infrared spectra of the molecules are simulated using the wavenumbers and the corresponding intensities obtained from the computations. The effect of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide, and water) is investigated. The integral equation formalism in the polarizable continuum model (IEF-PCM) is used for all solution phase computations.     

Spectroscopic characterization,X-ray structure and DFT studies on 4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]-N-methylthiazol-2-amine

The titled molecule 4-[3-(2,5-dimethylphenyl)-3-methylcyclobutyl]-N-methylthiazol-2-amine (C₁₇H₂₂N₂S) is synthesized and characterized by ¹H NMR, ¹³C NMR, IR, and X-ray single crystal determination. The compound crystallizes in the monoclinic space group P2_1/c with a = 6.3972(4) Å, b = 9.4988(6) Å, c = 26.016(2) Å and β = 93.496(7)°. In addition to the molecular geometry from the X-ray determination, vibrational frequencies and gauge, including the atomic orbital (GIAO), ¹H and ¹³C NMR chemical shift values of the titled compound in the ground state are calculated using the density functional (B3LYP) method with 6-31G(d), 6-31++G(d,p) and 6-311+G(2d,p) basis sets. The calculated results show that the optimized geometries can well reproduce the crystal structure. Moreover, the theoretical vibrational frequencies and chemical shift values show good agreement with the experimental values. The predicted nonlinear optical properties of the titled compound are greater than those of urea. DFT calculations of the molecular electrostatic potentials and frontier molecular orbitals of the titled compound are carried out at the B3LYP/6-31G(d) level of theory.     

A one-dimensional silver(I) coordination polymer with saccharin and pyrazine: synthesis,crystal structure,thermal analysis,FTIR spectra,and DFT studies

A silver(I) complex of saccharinate (sac) with pyrazine (pyz), [Ag(sac)(pyz)] _n , has been synthesized and characterized by elemental analysis, IR, thermal analysis, and single-crystal X-ray diffractometry. The complex crystallizes orthorhombic space group Pnma with unit cell parameters of a = 13.0073(9) Å, b = 6.4907(6) Å, c = 13.4007(9) Å, V = 1131.37(15) Å³, and Z = 4. [Ag(sac)(pyz)] _n is a one-dimensional coordination polymer, in which the sac ligand acts as a monodentate ligand through the N atom and the trigonal silver centers are linked by the bridging pyz ligands. The individual chains are connected into two-dimensional supramolemular network by aromatic π(sac)···π(pyz) stacking interactions. The FTIR spectrum of [Ag(sac)(pyz)] _n has been recorded in the region and 4,000–400 cm^?1. The optimized geometry, frequency, and intensity of the vibrational bands of [Ag(sac)(pyz)] _n were obtained by density functional theory (DFT) at the B3LYP level. The vibrational frequencies were calculated and the scaled values have been compared with the experimental FTIR data. The observed and calculated frequencies are found to be in good agreement.     

Fourier transform IR spectra and structure of 2-substituted 1-nitro- and 1-bromo-1-nitroethenes

Molecular structure and vibrational spectra of 2-trichloromethyl(ethoxycarbonyl)-1-nitroethenes and 2-trichloromethyl(ethoxycarbonyl)-1-bromo-1-nitroethenes were calculated in terms of the density functional theory (B3LYP/6-31G*). The experimental FTIR spectra of these compounds in the range from 4000 to 400 cm^?1 were interpreted in detail on the basis of the calculation data. 2-Substituted 1-nitro- and 1-bromo-1-nitroethenes were assigned the structure with trans orientation of the nitro and trichloromethyl (or ethoxycarbonyl) groups, and the ethoxycarbonyl derivatives were assumed to exist in equilibrium between s-cis and s-trans conformers.     

Theoretical and experimental study of molecular structure and vibrational spectra of <Emphasis Type="Italic">N</Emphasis>-(2-pyridylmethyl)-2-pyrazinecarboxamide

N-(2-Pyridylmethyl)-2-pyrazinecarboxamide was prepared and its crystal structure was investigated by X-ray analysis. The compound crystallizes in the triclinic space group \(P{\bar 1}\) with a = 4.262(3), b = 12.117(9), c = 20.840(18) Å, α = 91.802(6), β = 89.834(7), γ = 91.845(6)°, V = 1075.2(16) ų, Z = 4, and D = 1.323?Mg/m³. The structure was solved by direct method and refined to R = 0.0699 and wR ₂ = 0.1268 by full matrix anisotropic least-squares method. Using the Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set, the molecular geometry and vibrational frequencies of the title compound has been investigated and compared with experimental ones from experimental studies. The optimized bond lengths obtained by RHF method and bond angles obtained by B3LYP method show better agreement with the experimental values. The vibrations computed of the title compound by the RHF and DFT methods are in good agreement with the observed IR spectra data.     

Experimental and Theoretical Vibrational Spectra of Sideridiol Isolated from <Emphasis Type="Italic">Sideritis</Emphasis> Species

Sideridiol (ent-7α,18β-dihydroxykaur-15-ene) one of the ent-kaurene diterpenoid, is isolated from the genus Sideritis L. belongs to the family of Lamiaceae. The vibrational frequencies of sideridiol in the ground state have been calculated using the Density Functional Theory (DFT) method with the 6-31G(d) and 6 31+G(d,p) basis sets. The calculated vibrational frequencies have been compared with that of obtained experimental IR spectrum.     

Density functional theory studies of conformational stabilities and rotational barriers of 2- and 3-thiophenecarboxaldehydes

The molecular structures, conformational stabilities, and infrared vibrational wavenumbers of 2-thiophenecarboxaldehyde and 3-thiophenecarboxaldehyde are computed using Becke-3–Lee–Yang–Parr (B3LYP) with the 6-311++G** basis set. From the computations, cis-2-thiophenecarboxaldehyde is found to be more stable than the transfer conformer with an energy difference of 1.22 kcal/mol, while trans-3-thiophenecarboxaldehyde is found to be more stable than the cis conformer by 0.89 kcal/mol. The computed dipole moments, structural parameters, relative stabilities of the conformers and infrared vibrational wavenumbers of the two molecules coherently support the experimental data in the literature. The normal vibrational wavenumbers are characterized in terms of the potential energy distribution using the VEDA4 program. The effect of solvents on the conformational stability of the molecules in nine different solvents is investigated using the polarizable continuum model.     

DFT Study of the Molecular Structure,Conformational Preference,HOMO, LUMO,and Vibrational Analysis of 2-, and 3-Furoyl Chloride

Molecular structure, conformational stability and vibrational wave numbers for the rotational isomers of 2-furoyl chloride and 3-furoyl chloride have been computed using the B3LYP method with the 6-311++G(d,p) basis set. From computations, 2-furoyl chloride was predicated to exist predominantly in cis conformation with cis–trans rotational barrier 40.40 kJ·mol^?1, and 3-furoyl chloride was predicated to exist predominantly in the trans conformation with cis–trans rotational barrier 30.17 kJ·mol^?1. The effects of solvents on the conformational stability of all the molecules in nine different solvents (heptane, chloroform, tetrahydrofuran, dichloroethane, acetone, ethanol, methanol, dimethylsulfoxide and water) were investigated. The integral equation formalism of the polarizable continuum model was used for all solution phase computations. The vibrational wave numbers and the corresponding vibrational assignments of the molecules in C₁ symmetry were examined and the simulated infrared spectra of the molecules are reported. The geometrical parameters, highest occupied and lowest unoccupied molecular orbitals, Infrared intensities, and molecular electrostatic potentials results are reported.     

In Vitro Binding of Furadan to Bovine Serum Albumin

Under physiological conditions, the interaction between furadan (FRD) and bovine serum albumin (BSA) was investigated by spectroscopy including fluorescence emission, UV-visible absorption, scattering, circular dichroism (CD) spectra, synchronous and three-dimensional fluorescence spectra. The observed binding constant K _b and the number of binding sites n were determined by the fluorescence quenching method. The distance r between donor (BSA) and acceptor (FRD) was obtained according to the Förster theory of non-radiation energy transfer. The enthalpy change (ΔH ^θ ), Gibbs energy change (ΔG ^θ ) and entropy change (ΔS ^θ ) at four different temperatures were calculated. The process of binding was proposed to be a spontaneous process since the ΔG ^θ values were negative. The positive ΔS ^θ and ΔH ^θ values indicated that the interaction of FRD and BSA was driven mainly by hydrophobic interactions. The addition of FRD to BSA solutions leads to enhancement in scattering intensity, exhibiting the formation of an aggregate in solution. CD spectra, synchronous and three-dimensional fluorescence spectra were used to measure the structural change of BSA molecules with FRD present.     

Quantum Chemical Study of Niobium and Tantalum M<Subscript>4</Subscript>O<Subscript>10</Subscript> Oxide Clusters and M<Subscript>4</Subscript>O<Stack><Subscript>10</Subscript><Superscript>–</Superscript></Stack> Anions

Structural parameters and vibrational frequencies of the clusters (T_d)–Nb₄O₁₀, (C_3v)-TaNb₃O₁₀, (D_2d)-Nb₄O ₁₀ ^– , and (C_s)-TaNb₃O ₁₀ ^– were calculated. According to the (U)DFT/SDD calculations with BLYP, B3LYP, and PBE0 functionals magnetization of the anion (D_2d)-Nb₄O ₁₀ ^– is distributed equally among four niobium atoms. In the anion (C_s)-TaNb₃O ₁₀ ^– unpaired electron presumably occupies niobium atoms. The distinction in contributions from Nb atoms in the magnetization of the tantalum-containing cluster grows with the exchange component of the DFT functional in the series of functionals BLYP < B3LYP < PBE0 < UHF.     

Experimental and theoretical studies of diethyl 2-(<Emphasis Type="Italic">ter</Emphasis>-butylimino)-2,5-dihydro-5-oxo-1-phenyl-1H-pyrrole-3,4-dicarboxylate using DFT calculations

In this study, diethyl 2-(ter-butylimino)-2,5-dihydro-5-oxo-1-phenyl-1H-pyrrole-3,4-dicarboxylate compound 1 is synthesized and characterized by FT-IR, ¹H and ¹³C NMR spectroscopy. The DFT calculations are carried out for compound 1 by B3LYP and PBE1PBE methods. The bond lengths, bond angles, dihedral angles, charge density on the atoms of 1 are calculated. A comparison of the DFT calculations indicate that the B3LYP method with the 6-311G++(d,p) basis set can give accurate results. The ¹³C NMR and ¹H NMR chemical shifts of 1 are calculated and compared with the available experimental data on the molecules. The nuclear independent chemical shift (NICS) calculations are utilized for the pyrrole ring in compound 1.     

Microwave spectrum,centrifugal perturbation,dipole moment,and conformation of 5-methyl-1,3-dioxane

The microwave spectrum of 5-methyl-1,3-dioxane was studied in the frequency range 12–35 GHz. The a and c type rotation transitions with J≤30 were identified. The rotational constants A = 4658.5244(33) MHz, B = 2383.3930(12) MHz, and C = 1724.28907(88) MHz and the quartic constants of the centrifugal distortion of the molecule in the ground vibrational state were determined. The components of the dipole moment were found, μ _a = 1.76 ± 0.01 D and μ _c = 1.10 ± 0.01 D; the net dipole moment of the molecule is μ = 2.08 ± 0.01 D. 5-Methyl-1,3-dioxane was calculated by the B3PW91/aug-cc-pVDZ density functional theory method. The calculated data are compared with the experimental data. The most stable conformation is the chair conformation with an equatorial orientation of the methyl group.     

Volumetric,Viscometric and Speed of Sound Studies of Binary Mixtures of <Emphasis Type="Italic">Tert</Emphasis>-butyl Acetate with Fluorobenzene,Chlorobenzene and Bromobenzene at (298.15 and 308.15) K and at Atmospheric Pressure 0.087 MPa

Volumetric, viscometric and speed of sound studies of binary mixtures of tert-butyl acetate with fluorobenzene, chlorobenzene and bromobenzene have been made over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure (p?=?0.089 MPa). From the experimental values of density, viscosity, and speed of sound, the excess molar volumes V^E, deviations in viscosity ?η and deviation in isentropic compressibility ΔK _S have been calculated. The V^E and ΔK _S values are negative while the ?η the values are positive over the entire composition range for the binary mixtures. The derived parameters have been fitted with the Redlich–Kister polynomial equation. The interaction parameters of McAllister model are used to correlate the experimental values of density, viscosity and speed of sound.     

Quantum-chemical study of lutetium,ytterbium, and gadolinium phthalocyaninates PcLnCl

Structural parameters and IR spectra of the (¹A₁//C_4v)-PcLuCl, (²B₂//C_4v)-PcYbCl, and (⁸A₂//C_4v)-PcGdCl molecules, (²A₂//C_4v)-Pc⁺LuCl, (3B₁//C_4v)-Pc⁺YbCl, and (⁹A₁//C_4v)-Pc⁺GdCl cations, (¹A_g//D_2h)-PcLuCl₂LuPc dimer, and PcLuCl···PcLuCl coaxial molecular pair have been simulated using the DFT (U) PBE0/SDD method. The PcLnCl (Ln = Lu, Yb, Gd) molecules have exhibited the equilibrium Ln–N bond length of 222, 223, and 230 pm, the Ln–Cl bond length of 245, 246, and 253 pm, the dipole moment of 4.73, 4.57, and 4.84 D directed from Cl to Ln, and ionization potential of 6.6 eV. β-Decay (¹A₁//C_4v)-Pc¹⁷⁷LuCl → (¹A₁//C_4v)-(Pc^177mHfCl)⁺ occurs with no significant change of the charge on the metal atom.     

Tautomerism in the Sulfonamide Moiety: Synthesis,Experimental and Theoretical Characterizations

Following our previous work, we synthesized N-(7-methyl-5,6-diphenyl-2-m-tolyl-7H-pyrrolo[2,3-d]pyrimidin-4-yl)benzensulfonamides to study the sulfonylimine-sulfonamide tautomerism. This goal is performed using the density functional theory (DFT). Four plausible isomers including the keto and enol sulfonamide as well as Z and E sulfonimide are considered for each of compounds. The DFT calculations are carried out at the B3LYP/6-31+G(d,p) level of theory. The optimized geometric parameters such as bond lengths and bond angles are calculated. The computed IR vibrational frequencies and ¹H NMR chemical shifts are in good agreement with the experimental data. The structure of all compounds is confirmed on the basis of their full spectral data. In all three compounds, the Z-sulfonimide form is more stable than the other isomers. A high energy gap between the frontier orbitals confirms the stability of the compounds.     

Interpretation of the Parameters of the EPR Spectra of Transition Metal Complexes

The calculated parameters of the EPR spectra of complexes of d¹ and d⁹ ions were presented. The covalent bond parameters used in the calculations were determined from EPR and experimental optical data (inverse problem of EPR spectroscopy). Various contributions to the expressions for the EPR parameters were compared. The observed abnormal values of the EPR parameters were discussed. The effects of charge-transfer states and the vibronic coupling on the components of g, A, and A^L tensors were considered. Mechanisms of spin density transfer to ligands in paramagnetic complexes were proposed.     

Dynamic structure of organic compounds in solution according to NMR data and quantum mechanical calculations: I. Soman

Dynamic structure of Soman diastereoisomers has been studied with the goal of obtaining accurate information to simulate molecular mechanisms of its action on living systems. The potential energy surface for internal rotation about the single P–O and O–C bonds has been constructed in terms of the Møller–Plesset second-order perturbation theory using 6-311G(d,p) basis set. The relative contributions of different conformers have been estimated by solving the vibrational problem according to the large-amplitude vibration model. The conformational dependences of the ⁴J_CF and ³J_CP coupling constants for the S,S and S,R diastereoisomers of Soman have been calculated at the FPT DFT B3LYP/6-311++G(2df,2p) level of theory. The calculated vibrationally averaged coupling constants have been compared with the available experimental data to determine the structure of the most toxic Soman stereoisomer.     

<Emphasis Type="Italic">N</Emphasis>-allyl and <Emphasis Type="Italic">N</Emphasis>-propargyl trifluoromethanesulfonimides. Theoretical analysis

Tautomers of N-allyl- and N-propargyl-substituted trifluoromethanesulfonimides (CF₃SO₂)₂NR (R = CH₂CH=CH₂, Z/E-CH=CHMe, CH₂C≡CH, CH=CH=CH₂, C≡CCH₂) were calculated by the DFT (B3LYP, wB97XD, PBE1PBE), MP2, and CBS-QB3 methods. The results were compared with the theoretical data for the corresponding amines and amides NHRR¹ (R¹ = H, CF₃SO₂). It was shown that there is no conjugation between the nitrogen atom and C=C bond and that conjugation exists with the C≡C bond with electron density displacement toward the nitrogen atom. The calculations of anions derived from N-allyl- and N-propargyl-trifluoromethanesulfonimides revealed the possibility of their rearrangement with elimination of trifluoromethanesulfinate anion and formation of its H-complex with N-(prop-2-en-1-ylidene)trifluoromethanesulfonamide or N-(prop-2-yn-1-ylidene)trifluoromethanesulfonamide.     

Theoretical studies on the structural,spectroscopic, thermodynamic,and electronic properties of zoledronic acid

The structure, spectroscopic, thermodynamic, and electronic properties of zoledronic acid (ZL, 1-hydroxy- 2-(1H-imidazol-1-yl)ethane-1,1-diyldiphosphonic acid), typical third-generation nitrogen-containing bisphosphonates (N-BPs), have been investigated systematically. Six conformations are taken into account, including three unprotonated and three protonated structures. They are optimized by four different density functional theory (DFT) methods combined with four different basis sets to evaluate their performance in predicting the structural and spectral features of ZL. Thermodynamic properties are calculated based on the harmonic vibrational analysis, including the standard heat capacity (C _p,m ⁰ ), entropy (S _m ⁰ ), and enthalpy (S _m ⁰ ). The ¹H and ¹³C NMR chemical shifts are calculated using the GIAO method and compared with the experimental data. Molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) analyses are also performed to study the electronic characteristics of the title compound.