1H NMR analysis of O‐methyl‐inositol isomers: a joint experimental and theoretical study

Density functional theory (DFT) calculations of ¹H NMR chemical shifts for l ‐quebrachitol isomers were performed using the B3LYP functional employing the 6‐31G(d,p) and 6‐311 + G(2d,p) basis sets. The effect of the solvent on the B3LYP‐calculated NMR spectrum was accounted for using the polarizable continuum model. Comparison is made with experimental ¹H NMR spectroscopic data, which shed light on the average uncertainty present in DFT calculations of chemical shifts and showed that the best match between experimental and theoretical B3LYP ¹H NMR profiles is a good strategy to assign the molecular structure present in the sample handled in the experimental measurements. Among four plausible O‐methyl‐inositol isomers, the l ‐quebrachitol 2a structure was unambiguously assigned based only on the comparative analysis of experimental and theoretical ¹H NMR chemical shift data. The B3LYP infrared (IR) spectrum was also calculated for the four isomers and compared with the experimental data, with analysis of the theoretical IR profiles corroborating assignment of the 2a structure. Therefore, it is confirmed in this study that a combined experimental/DFT spectroscopic investigation is a powerful tool in structural/conformational analysis studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantum‐chemical,IR, NMR,and X‐ray diffraction studies on 2‐(4‐chlorophenyl)‐1‐methyl‐ 1H‐benzo[d]imidazole

The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C₁₄H₁₁ClN₂), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO ¹H and ¹³C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. ¹³C and ¹H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

An experimental and theoretical approach to the molecular structure of 3‐{[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐ indol‐2‐one

The title molecule, 3‐{[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐indol‐2‐one (C₂₂H₂₀N₄O₁S₁), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, UV–visible, and single‐crystal X‐ray diffraction. The compound crystallizes in the monoclinic space group P21 with a = 8.3401(5), b = 5.6976(3), c = 20.8155(14) Å, and β = 95.144(5)°. Molecular geometry from X‐ray experiment and vibrational frequencies of the title compound in the ground state has been calculated using the Hartree–Fock with 6‐31G(d, p) and density functional method (B3LYP) with 6‐31G(d, p) and 6‐311G(d, p) basis sets, and compared with the experimental data. The calculated results show that optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies values show good agreement with experimental data. Density functional theory calculations of the title compound and thermodynamic properties were performed at B3LYP/6‐31G(d, p) level of theory. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Struktur und Eigenschaften des Hydridomethyltetrafluorphosphatanions, [CH3PF4H]—

Structure and Properties of the Hydridomethyltetrafluorophosphate Anion, [CH₃PF₄H]^— Methyltrifluorphosphorane reacts with strong fluoride donors like CsF, (CH₃)₄NF and (CH₃)₄PF with formation of the corresponding hydridomethyltetrafluorophosphates. The salts are characterized by NMR, IR and Raman spectroscopy. The experimental results show that only the trans isomer is formed. For both isomers theoretical calculations (B3LYP/6‐31+G* and RHF/6‐31+G*) were carried out. The difference for the Gibbs free energy between the isomers was calculated to be 35.4 kJ/mol (B3LYP/6‐31+G*). The RHF/6‐31+G* calculation yields, for the almost octahedral trans isomer, bond distances of r(PF) = 167 pm, r(PC) = 184.5 pm and r(PH) = 138.1 pm.     

Synthesis and Computational Study of Phosphorus Ionic Liquids

The synthesis of six tetraalkylammonium bromopentachlorophosphoride ionic liquids (ILs) is reported here. Their structures were determined by IR, ¹H NMR, and ¹³C NMR spectroscopy. Moreover, thermogravimetric (TG) and differential thermal analysis (DTA) were used to investigate the thermal behavior of these compounds. The results show that these ILs have excellent thermal stability below 145°C, and by decreasing the size of the alkyl groups, the thermal stabilities will increase. Along with the experimental study, these compounds have been studied computationally at the B3LYP/LANL2DZ level of theory using the PC GAMESS/Firefly program package. From these calculations, optimized geometries, molecular parameters, and vibrational spectra of ILs have been calculated. In addition, calculated frequencies are compared with the experimental frequencies after correction by the appropriate scaling factor. This comparison shows that our theoretical data are in good agreement with the experimental results.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Theoretical Simulation of Vibrational Sum‐Frequency Generation Spectra from Density Functional Theory: Application to p‐Nitrothiophenol and 2,4‐Dinitroaniline

The molecular orientation of adsorbed molecules forming self‐assembled monolayers can be determined by combining vibrational sum‐frequency generation (SFG) measurements with quantum chemical calculations. Herein, we present a theoretical methodology used to simulate the SFG spectra for different combinations of polarizations. These simulations are based on calculations of the IR vectors and Raman tensors, which are obtained from density functional theory computations. The dependency of the SFG vibrational signature with respect to the molecular orientation is presented for the molecules p‐nitrothiophenol and 2,4‐dinitroaniline. It is found that a suitable choice of basis set as well as of exchange‐correlation (XC) functional is mandatory to correctly simulate the SFG intensities and consequently provide an accurate estimation of the adsorbed molecule orientation. Comparison with experimental data shows that calculations performed at the B3LYP/6‐311++G(d,p) level of approximation provide good agreement with experimental frequencies, and with IR and Raman intensities. In particular, it is demonstrated that polarization and diffuse functions are compulsory for reproducing the IR and Raman spectra, and consequently vibrational SFG spectra, of systems such as p‐nitrothiophenol. Moreover, the investigated XC functionals reveal their influence on the relative intensities, which show rather systematic variations with the amount of Hartree–Fock exchange. Finally, further aspects of the modeling are revealed by considering the frequency dependence of the Raman tensors.     

Synthesis, characterization, crystal structure and DFT studies on 1',3'-dihydrospiro[fluorene-9,2'-perimidine

The title compound, 1′,3′-dihydrospiro[fluorene-9,2′-perimidine] has been synthesized and characterized by NMR, ESI-MS, IR, elemental analysis, UV–vis and fluorescence spectroscopy. The crystal structures of the title compound and its co-crsytal with 9-fluorenone have also been determined by X-ray single crystal diffraction. Density functional theory (DFT) calculations and vibrational frequencies have been performed at B3LYP/6-31G* level. The comparisons between the experimental vibrational frequencies and the predicted data show that B3LYP/6-31G* method can simulate the IR of the title compound on the whole. The theoretical electronic absorption spectra have been calculated by using TD-DFT method and compared with the experimental result. The solid-fluorescence determination of the title compound reveals two emission bans at 430 and 590 nm while its co-crystal reveals only one emission band at 590 nm.     

Solvent influence on the rotational isomerism in terephthalaldehyde

Experimental and theoretical studies were carried out in order to investigate the rotational isomerism of terephthalaldehyde. The dipole moment measurements and infrared spectroscopy in Ar matrix and using various solvents were performed experimentally. In order to supplement the experimental study, both static and dynamical theoretical calculations were performed. IR spectra and potential energy distribution (PED) were calculated for both cis and trans isomers of terephthalaldehyde in gas phase using B3LYP/6-31G(d,p) level of theory. Further calculations consisted of conformational analysis were performed in order to estimate the rotational barrier and relative stabilities of isomers. The DFT theory with B3LYP functional and four double-zeta and triple-zeta basis sets served as framework for this part of calculations. Semiempirical AM1 and PM3 methods were also used for gas-phase modeling. Molecular dynamics using MM3 force field was applied to study the preferences of solvent molecules’ orientation around the studied molecule. Additionally, the effect of solvent polarity on the Gibbs energy of the trans ⇌ cis equilibrium was analyzed in terms of the continuum dielectric medium models.     

DFT‐GIAO 1H and 13C NMR prediction of chemical shifts for the configurational assignment of 6β‐hydroxyhyoscyamine diastereoisomers

¹H and ¹³C NMR chemical shift calculations using the density functional theory–gauge including/invariant atomic orbitals (DFT–GIAO) approximation at the B3LYP/6‐311G++(d,p) level of theory have been used to assign both natural diastereoisomers of 6β‐hydroxyhyoscyamine. The theoretical chemical shifts of the ¹H and ¹³C atoms in both isomers were calculated using a previously determined conformational distribution, and the theoretical and experimental values were cross‐compared. For protons, the obtained average absolute differences and root mean square (rms) errors for each comparison showed that the experimental chemical shifts of dextrorotatory and levorotatory 6β‐hydroxyhyoscyamines correlated well with the theoretical values calculated for the (3R,6R,2′S) and (3S,6S,2′S) configurations, respectively, whereas for ¹³C atoms the calculations were unable to differentiate between isomers. The nature of the relatively large chemical shift differences observed in nuclei that share similar chemical environments between isomers was asserted from the same calculations. It is shown that the anisotropic effect of the phenyl group in the tropic ester moiety, positioned under the tropane ring, has a larger shielding effect over one ring side than over the other one. Copyright © 2009 John Wiley & Sons, Ltd.     

Density‐functional Theory on the Oxidation Potentials and Geometry Parameters of Thioxanthen Derivatives: Theory and Experiment

Abstract

DFT calculations were performed for 1‐fluoro‐4‐hydroxy‐thioxanthen‐9‐one (FHT) and 1‐Hydroxy‐3,4‐dimethyl‐thioxanthen‐9‐one (HDT). The calculated IR spectrum of FHT and HDT were used for the assignment of IR frequencies that were observed in the experimental IR spectrum. The bond lengths and bond angles for FHT and HDT compounds were optimized at B3LYP/6‐31G(d) level of the theory. Cyclic voltammetry of FHT and HDT solutions shows that oxidation electrode potentials of FHT and HDT are 809 and 1214 mV respectively. The electrode potentials were calculated using the solvation energies and the sum of electronic and thermal free energies of FHT and HDT. The theoretical and experimental values of the electrode potentials for the studied compounds are in excellent agreement.     

Are there reliable DFT approaches for 13C NMR chemical shift predictions of fullerene C60 derivatives?

The relationships between experimental and theoretical ¹³C NMR chemical shifts of a pristine fullerene C₆₀, monoadducts from [2 + n] cycloaddition (n = 1–3), and one [2 + 1] bis‐adduct are systematically analyzed for the first time by using diverse quantum‐chemical levels of theory. These levels involved B3LYP, B3PW91, B97‐2, mPW1PW91, PBE1PBE, and X3LYP hybrid functionals combined with 3‐21G, 6‐31G, 6‐31G(d), 6‐31G(d,p), 6‐31G(d,2p), LanL2DZ, and SDDAll basis sets. X3LYP/6‐31G approach is determined to have the lowest deviations from the ¹³C NMR experimental data compared to the other methods for all the fullerene compounds (mean absolute error value is 0.856 ppm and root mean squared error value is 1.197 ppm). The highest deviations are characteristic for α (sp² C2/C5/C8/C10) and β (sp² C6/C7/C11/C12) carbon atoms relative to a functionalization site and for those (sp³ C1/C9) directly attached with a side fragment in the [2 + n] monoadducts (n = 1–3). A probable reason of such deviation is that the approaches do not take into account a contribution of paramagnetic ring currents to ¹³C NMR chemical shifts. The results will be useful in design of novel fullerene derivatives and in performing unambiguous ¹³C NMR chemical shift assignments with modern quantum chemistry calculations.     

Stabilization in neutral bicyclic sulfoxide compounds

Density Functional Theory (DFT) calculations at the B3LYP/6‐31+G* level have been performed on 5‐thiabicyclo[2.1.1]hex‐2‐ene S‐oxide derivatives. The geometrical and electronic properties of the compounds have been analyzed in order to explain the favored stability of the exo configuration. Isodesmic reactions at the Gaussian‐G2 theory yielded the exo conformer as the most stable one. Moreover, the NMR chemical shift parameters (GIAO method) together with the Atoms in Molecules theory reveal an stabilization of the S atom with the double bond for the exo configuration, in agreement with the experimental results. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 322–327, 2000     

Comparative studies on the structures,infrared spectrum,and thermodynamic properties of phthalocyanine using ab initio Hartree–Fock and density functional theory methods

The molecular structure, vibrational spectrum, standard thermodynamic functions, and enthalpy of formation of free base phthalocyanine (Pc) have been studied using the density functional theory B3LYP procedure, as well as the ab initio Hartree–Fock method. Various basis sets 3‐21G, 6‐31G*, and LANL2DZ have been employed. The results obtained at various levels are discussed and compared with each other and with the available experimental data. It is shown that calculations performed at the Hartree–Fock level cannot produce a reliable geometry and related properties such as the dipole moment of Pc and similar porphyrin‐based systems. Electron correlation must be included in the calculations. The basis set has comparatively less effect on the calculated results. The results derived at the B3LYP level using the smaller 3‐21G and LANL2DZ basis sets are very close to those produced using the medium 6‐31G* basis set. The geometry of Pc obtained at the B3LYP level has D_2h symmetry and the diameter of the central macrocycle is about 4 Å. The enthalpy of formation of Pc in the gas phase has been predicted to be 1518.50 kJ/mol at the B3LYP/6‐311G(2d,2p)//B3LYP/6‐31G* level via an isodesmic reaction. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

GIAO/DFT studies on 1,2,4‐triazole‐5‐thiones and their propargyl derivatives

Density functional theory (DFT)/Becke–Lee–Yang–Parr (B3LYP) and gauge‐including atomic orbital (GIAO) calculations were performed on a number of 1,2,4‐triazole derivatives, and the optimized structural parameters were employed to ascertain the nature of their predominant tautomers. ¹³C and ¹⁵N NMR chemical shifts of 3‐substituted 1,2,4‐triazole‐5‐thiones and their propargylated derivatives were calculated via GIAO/DFT approach at the B3LYP level of theory with geometry optimization using a 6‐311++G** basis set. A good agreement between theoretical and experimental ¹³C and ¹⁵N NMR chemical shifts could be found for the systems investigated. The data generated were useful in predicting ¹⁵N chemical shifts of all the nitrogen atoms of the triazole ring, some of which could not be obtained in solution state ¹⁵N HMBC/HSQC NMR measurements. The energy profile computed for the dipropargylated derivatives was found to follow the product distribution profile of regioisomers formed during propargylation of 1,2,4‐triazole thiones. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectroscopic, quantum chemical DFT/HF study and synthesis of [2.2.1] hept-2'-en-2'-amino-N-azatricyclo [3.2.1.0(2,4)] octane

The compound 4-N-bicyclo [2.2.1] hept-2'-en-2'-amino-N-azatricyclo [3.2.1.0(2,4)] octane (2) has been synthesized and characterized by elemental analysis, IR, UV-vis, mass and NMR. Density functional theory (DFT) and Hartree-Fock (HF) calculations have been carried out for the title compound by using the standard 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. Predicted vibrational frequencies have been assigned and compared with experimental IR spectra and they complement each other. The theoretical electronic absorption spectra have been calculated by using CIS, TD-DFT and ZINDO methods. The (13)C NMR and (1)H NMR of compound (2) have been calculated by means of Becke 3-Lee-Yang-Parr (B3LYP) density functional method with 6-31G* basis set. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated.     

Conformational preferences of N-acetyl-L-leucine-N'-methylamide. Gas-phase and solution calculations on the model dipeptide

A DFT study of N-acetyl-l-leucine-N'-methylamide conformers in the gas phase and in solution was carried out. The theoretical computational analysis revealed 43 different conformations at the B3LYP/6-31G(d) level of theory in the gas phase. In addition, the effects of three solvents (water, acetonitrile, and chloroform) were included in the calculations using the isodensity polarizable continuum model (IPCM) and the Poisson-Boltzmann self-consistent reaction field (PB-SCRF) method. The stability order of the different conformers in solution has been analyzed. The theoretical results were compared with some experimental data (X-ray, IR, and NMR).     

Theoretical and experimental studies on solubility and reactivity behavior of lysergol,elymoclavine, and dihydrolysergol

Lysergol, elymoclavine (Δ^9,10 and Δ^8,9 regioisomers), and dihydrolysergol are important members of ergolines. The present work reports their comparative study in gas and solvent phase (water) that has been performed both experimentally and theoretically. Theortical calculations have been carried within the density functional theory formalism to analyze the structural and electronic properties of these molecules with B3LYP hybrid exchange–correlational fuctional in conjunction with 6‐311++G (d,p) basis set. Hessian calculations are performed at B3LYP/6‐31G (d,p) level of theory in gas phase as well as other solvent phases. Solvent phase calculations are performed using Onsager reaction field model as implemented in Gaussian 03. A good agreement has been found between experimental and theoretical infrared and nuclear magnetic resonance (NMR) spectra. The calculated NMR data has been analyzed statistically. Stability of these regioisomers has been analyzed in terms of the energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO gap). Calculations for lysergol and elymoclavine in water as solvent were carried to examine the effect of solvent on the HOMO–LUMO levels and energy of these molecules. © 2012 Wiley Periodicals, Inc.     

A Photosensitive Liquid Crystal Studied by 14N NMR, 2H NMR,and DFT Calculations

An azobenzene derivative, namely diheptylazobenzene, showing the nematic and smectic A liquid crystalline phases, was investigated by means of a combined approach based on NMR and DFT calculations. ¹⁴N NMR quadrupole‐ and chemical‐shift‐perturbed spectra were acquired in the whole mesophasic range, providing both experimental quadrupolar splittings and chemical shift anisotropy values. On the same mesogen, deuterium labelled at the α‐position of the hydrocarbon chain, ²H NMR quadrupole‐perturbed spectra were recorded. The analysis of these NMR data was performed with the help of ab initio calculations, in vacuo and by taking into account the effect of the anisotropic environment typical of liquid crystals, by using the IEF‐PCM model. The geometry optimizations of the azomesogen in the trans and cis configurations were performed by DFT calculations employing the combination of B3LYP functional with the 6‐311G(d) basis set. The analysis of experimental NMR data was performed by considering the trans configuration as the most populated one and the corresponding quadrupolar tensors and chemical shielding tensors were determined at the DFT level of theory. The main result of this work is the determination of a relatively high and temperature‐dependent molecular biaxiality of the trans state of this azomesogen.     

Synthesis,Density Functional Theory Band Structure Calculations,Optical, and Photoelectrical Characterizations of the Novel (9‐Bromo‐3‐cyano‐5‐oxo‐1,5‐dihydro‐2H‐chromeno[4,3‐b]pyridin‐2‐ylidene)propanedinitrile

Ring transformation of 6‐bromochromone‐3‐carbonitrile ( 1 ) with malononitrile dimer in basic medium furnished the unexpected (9‐bromo‐3‐cyano‐5‐oxo‐1,5‐dihydro‐2H‐chromeno[4,3‐b]pyridin‐2‐ylidene)propanedinitrile ( 2 , BCOCPP ). Density functional theory, theoretical investigation of the electronic structure, geometries linear polarizability ?Δα? (Quadrupole moment), first‐order hyperpolarizability ?β? (Octapole moment), natural bonding orbital, molecular electrostatic potential contours, thermo‐chemical parameters, harmonic vibration frequencies, the FT‐IR spectrum of the compound ( 2 , BCOCPP ) in the solid phase was recorded, and time‐dependent density functional theory calculations at the B3LYP/6‐311G (d,p) level of theory, UV‐Vis spectra, in both ethanol and dioxane solvents have been employed for compound ( 2 , BCOCPP ). The geometrical and energetic parameters have been extensively investigated to reveal the reason behind the selective formation of compound ( 2 , BCOCPP ), instead of expected product 3 . The Coulomb‐attenuating method‐B3LYP and Corrected Linear Response Polarizable Continuum Model studied for theoretically obtaining the electronic absorption spectra in gas phase, ethanol, and dioxane, respectively, and indicate a good agreement with the observed spectra. The heterojunction based on BCOCPP showed phototransient properties under various illumination intensities that give the recommendation of the studied heterojunction in the field of optoelectronic device application.