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The present work deals with the understanding of the integrated experimental and theoretical study of the molecular structure and vibrational spectra of N-allyl-N-ethylformamide (NAEF). Density functional theory (DFT) calculations were used to study the subject molecule, N-allyl-N-ethylformamide (NAEF), utilising the B3LYP method and the basis set 6-311++G (d,p). Geometrical parameters and the structure of NAEF were computed such that global descriptors and reactive sites were obtained. Frontier's analysis of molecular orbital energy demonstrates that the molecule's charge exchange is considerably high. Non-linear optical properties of N-allyl-N-ethylformamide (NAEF) were computed and compared with the standard material of urea. The vibrational assignments were analysed for the existence of the probable functional groups and tabulated. The thermodynamic functions were computed at different temperatures and listed accordingly. NMR spectroscopy and quantum computational chemistry methods have been employed for the understanding of the structures of NAEF. Moreover, different techniques such as topological analysis and drug-likeness were utilised to determine the structure and other properties of NAEF. The molecular docking study could determine the residue with the highest docking score (lowest binding energy) and the most non-covalent interactions. [ABSTRACT FROM AUTHOR]

The molecular structure of 1-(4-hydroxy-3-methoxyphenyl) ethenone has been optimized, and its various parameters were ascertained, using Density Functional Theory. The molecule's Fourier Transform-Infra Red and Raman spectra are recorded and examined. By comparing the computational and experimental results, molecular structure, bond length, and vibrational band intensity were all interpreted. The Integral Equation Formalism polarizable continuum model's depictions of electronic and Frontier Molecular Orbital solvent interaction investigations are sported to perceive the charge transfer among the atoms of the molecule in eco-green solvents such as water, acetone, and ethanol. The reactivity sites can be studied by locating and charting the electron density on the surface. The compound's hardness, softness, electrophilicity, and ionization potential were all analyzed. The pharmacological effects and intra-molecular hyper conjugative interactions are liable for its molecular stability, as shown by Natural Bond Orbital research. Topological studies, including Electron Localized Function, Localized Orbital Locator, and Reduced density gradient analysis, were performed to locate the compound's bonding area and Vander Waals interactions. Urea was used as a reference compound to examine the substance's non-linear optical characteristics. Total Density of States has investigated the role of molecular orbitals. Drug-likeness, a Ramachandran plot, and molecular docking were also performed to further analyze 1-(4-hydroxy-3-methoxyphenyl) ethanone's biological activity. The docking results lend credence to the idea that the title compound could function as a powerful cancer treatment. [ABSTRACT FROM AUTHOR]

An investigation into the properties of the novel compound with thioether-bridge 2-((4,5-di-p-tolyl-4H-1,2,4-triazol-3-yl)thio)-1-mesitylethanone by use of single-crystal X-ray diffraction (SCXRD), FT-IR, and nuclear magnetic resonance spectroscopy and density functional theory calculations. The X-ray crystallographic data, which reveal the molecular and crystal structure, have been collected in the 2.98–26.27 θ range at 296 K. Then, Hirshfeld surface analyses were performed over the crystal structure and possible hydrogen bondings were indicated. In addition to the determination of the structure, characteristic vibrational modes, chemical shifts (1H and 13C), and theoretical highest occupied molecular orbital–lowest unoccupied molecular orbital and UV analysis in four different solvents were evaluated. The structural and spectral results were compared with the corresponding quantum chemical calculations. The experimental and theoretical (calculated) data exhibited good harmony. Additionally, Natural Bonding Orbital and Mulliken charge analyses were investigated. Then, the molecular docking of the title ligand within the Protein Data Bank: 2IJ5 protein was evaluated according to interaction shapes. Lastly, drug-likeness and ADME features of the title molecule were evaluated. [ABSTRACT FROM AUTHOR]

A pyrazole ring derivative 5-(4-fluorophenyl)-1H pyrazole-3-amine was synthesized. The title compound was characterized by 1H NMR, 13C NMR, MS, FT-IR, and single crystal X-ray diffraction. The optimized molecular crystal structure was determined by B3LYP/6-311 + G(2d, p) functional method and based on density functional theory (DFT) calculation. Hirshfeld surface analysis illustrates the study of non-covalent interactions in the title compound. The molecular electrostatic potential (MEP) and major molecular orbitals (FMOs) of the title compounds were analyzed by computational method. Finally, infrared vibration analysis was performed on the target compound. [ABSTRACT FROM AUTHOR]

An indole compound, tert-butyl 6-chloro-3-(4,4,5,5-tetramethyl-1,3,2- dioxaborolan-2-yl)-1H-indole-1-carboxylate, was synthesized by a simple and efficient three-step substitution reaction. The structure of compounds can not be determined without the most common methods, namely, 1H NMR, 13C NMR, IR, MS. The structure of the target compound was determined by the above methods. Besides, the single crystal was obtained by solvent evaporation method, and the crystal structure data were obtained by means of X-ray diffraction and compared with the molecular crystal structure determined by density functional theory (DFT). Frontier molecular orbitals and molecular electrostatic potential energy are crucial in the study of chemical properties. [ABSTRACT FROM AUTHOR]

In this research work, Density Functional Theory based computational analysis on the molecular structure of Divalproex Sodium was carried out in the gas phase. Comprehensive analysis of vibrational spectra, Proton and Carbon Nuclear Magnetic Resonance, and electronic absorption spectrum have been carried out and the findings were compared to those obtained using computational techniques. The electronic transport properties were studied by the Ultraviolet-Visible spectrum obtained in distinct solvents by Time Dependent-Density Functional Theory method. Also, inter and intra-molecular interactions and charge transfer activity within the system were studied by Natural Bond Orbital and Frontier Molecular Orbital analyses. For the Non-Linear Optical profile of the compound, hyperpolarizability calculations were performed. The chemical reactivity of the investigated substance has also been disclosed by reactivity descriptors. The biological assessment through drug-likeness characteristics and molecular docking studies was performed to find the compound as anticonvulsant drugs. Optimized geometrical parameters were computed Vibrational, Electronic, and NMR spectra have been analyzed. Stability and chemical reactivity were studied. Inter/intramolecular interactions have been observed. Pharmacological activities were reported. [ABSTRACT FROM AUTHOR]

Benzenesulfonamide compounds containing piperazine heterocycles have prospective pharmacological activity. Two benzenesulfonamide compounds were synthesized. Based on density functional theory (DFT), the optimized structures of the two molecules were calculated using the B3LYP method. DFT was also used for further study of the molecular electrostatic potential and leading molecular orbital. Single crystal of 1-ethyl-4-(phenylsulfonyl)piperazine was studied. The intermolecular interaction and contact were quantified using Hirshfeld surface analysis and 2D fingerprint plots. Conformational analysis showed that the molecular structure after DFT optimization was consistent with the crystal structure determined by x-ray single crystal diffraction. [ABSTRACT FROM AUTHOR]

In this study, 1-(2-bromo-4-(dimethylamino)phenyl)-4-(2-chlorobenzyl)-[1,2,4] triazolo[4,3-a]quinazolin-5(4H)-one was synthesized via a five-step reaction and its single-crystal was obtained via solution crystallization, which was followed by crystallographic analysis. The molecular structure was calculated using density functional theory (DFT) and conformational analysis showed that the optimized molecular structure from DFT was comparable with that elucidated using X-ray diffraction. At the same time, the physicochemical properties of the compound could be understood by analyzing its frontier molecular orbitals and molecular electrostatic potentials. [ABSTRACT FROM AUTHOR]

In this study, N-(1,1′-biphenyl)-2-chlorobenzoylthiourea (HL) and its metal complexes were prepared and their structural characterization was made using elemental analysis, FT-IR, 1HNMR, HR-MS, single crystal XRD techniques, and TG/DTA analysis. The crystal structure of HL was investigated using single crystal X-ray diffraction and was observed to crystallize in the monoclinic crystal system with P 1 21/c 1 space group, Z = 4, a = 7.3291(4) Å, b = 20.7880(10) Å, c = 12.0074(6) Å. The structures of the complexes and the molecular orbitals of HL were optimized at B97D/TZVP level. Investigation of the thermal and electrochemical behaviors of the Co(II), Ni(II), and Cu(II) complexes were found to be thermally stable up to 165, 185, and 122 °C, respectively. Cell viability test MTT was made to determine anticancer activities against MCF-7 breast cancer cells and 2,2-diphenyl-1-picrilhydrazyl and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid analysis for the antioxidant activity. The IC50 values against MCF-7 cells and was found to be in the range 24.3–49.2 µM. [ABSTRACT FROM AUTHOR]

A series of cyclometalated platinum (II) complexes with aromatic ligands, such as pyridyl, pyrimidinyl, and pyrazolate, were investigated with theoretical calculations. To investigate the relationship between ligands with molecular orbital, molecular rigidity, electroluminescent properties, and spectroscopic properties, the electrostatic potential (ESP), density-of-states (DOS), and root mean squared displacement (RMSD) were calculated. On the basis of calculated absorption and phosphorescence data, the analysis of 'hole' and 'electron' have also been performed. From the RMSD and spin–orbit coupling (SOC) matrix elements calculations, complex 3 shows significant structural distortions on S1 state and it may be applied in thermal activation delayed fluorescence (TADF) materials. The electroluminescent properties calculations show that complex 1 is suitable for hole transport material and complex 4 can be applied to electron transport material. [ABSTRACT FROM AUTHOR]

Circularly polarised thermally activated delayed fluorescence (CP-TADF) molecules producing circularly polarised light which is beneficial to human eyes are widely used in circularly polarised organic light-emitting diodes. However, the relationship between the molecular structures and their luminescence properties of these CP-TADF molecules has not been well explained. Herein, the chiral molecule (R)-SFST with properties of circularly polarised luminescence (CPL) and thermally activated delayed fluorescence (TADF) is studied in detail. Firstly, we found two conformations by using molecular dynamic conformation search for (R)-SFST, namely (R)-SFST-a and (R)-SFST-b. The molecular geometric structures of singlet and triplet states are optimised by utilising density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Combining the thermal vibration correlation function methods, their photophysical properties are studied simultaneously. The processes of excited-state energy decay are revealed. The results show that the chiral units are more important to the molecular orbitals when the molecule has a more distorted configuration, which is beneficial to obtain CPL properties. However, when the molecular has rigid configuration, the excitons are easier to convert between S1 and T1, and the molecular has better TADF properties. Our results reveal the influence of different molecular conformations on CPL and TADF properties. [ABSTRACT FROM AUTHOR]

In the present study, we report the combined experimental and computational study along with antimicrobial screening of two tri-fluorinated chalcones from 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)ethan-1-one. The (E)-1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(4-(trifluoromethyl)phenyl)prop-2-en-1-one (DBTFP-1) and (E)-1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(4-(trifluoromethoxy)phenyl)prop-2-en-1-one (DBTFP-2) were synthesized by the famous Claisen-Schmidt condensation reaction. The computational investigation of optimized molecular structures, bond lengths and bond angles were performed by using density functional theory (DFT) with a B3LYP functional and 6-31G(d,p) basis set. The electronic properties were computed using Time-Dependent density functional theory (TD-DFT) with a B3LYP functional and 6-31G(d,p) basis set for the optimized geometries. The lower band gap in DBTFP-1 demonstrated the inevitable intramolecular charge transfer. The UV-Visible simulations were performed in the gas phase and dichloromethane (DCM) solvent. The experimental UV-Visible analysis was performed in DCM solvent. The first singlet excited state was attributed to the n-π* and second singlet excited state to the π -π* electronic transition. The scaled vibrational bands of titled compounds were compared with experimental observations and correct vibrational assignments were made. Various global reactivity parameters were analyzed and discussed to apprehend the chemical behavior of the synthesized chalcones. MESP and contour surfaces revealed negative potentials near the oxygen atoms and positive potentials over the hydrogen atoms. Mulliken charge study revealed that C17 and C33 are the most negative and positive carbon atoms in DBTFP-1, respectively, whereas C17 and C35 are the most negative and positive carbon atoms in DBTFP-2. The antibacterial activity was performed against P. vulgaris and S. aureus and antifungal activity against A. niger and C. albicans. The antimicrobial activity for these two compounds was correlated with LUMO and band gap energy. The magnificent antimicrobial activity of DBTFP-1 was attributed to its more stabilized LUMO and lower band gap than DBTFP-2. [ABSTRACT FROM AUTHOR]

The geometrical structures and bonding properties of anionic, neutral, and cationic B3Ge12 clusters are investigated by quantum chemical calculations. The lowest-lying isomer of B 3 Ge 12 − anion is found to have a distorted B-endohedral pentagonal prism with two face-capping B atoms and two face-capping Si atoms. In particular, B 3 Ge 12 − anion is an outstanding superatom cluster with closed-shell electronic configuration of 1S21P61D102S21F142P61G18 on the principle of jellium model. Global minimum of B3Ge12 neutral adopts a D3h symmetric hexagonal prismatic structure with a B3 triangle at the centre being parallel to the two hexagons and has strong B–B bonding interactions, being very close to the typical B−B single bond. B 3 Ge 12 + cation has a similar structural feature with its neutral corresponding counterpart. Moreover, the nucleus-independent chemical shift (NICS), aromatic stabilisation energy (ASE), and multicenter bond index calculations suggest B3Ge12 neutral to be aromatic. Furthermore, the molecular orbitals reveal that B3Ge12 neutral exhibits σ plus π double bonding characters. Electrons are transferred from Ge12 framework to B atoms in terms of natural population analysis (NPA), atoms in molecules (AIM), and atomic dipole moment corrected Hirshfeld (ADCH) population analyses. [ABSTRACT FROM AUTHOR]

The conformational study using Potential Energy Surface analysis was performed and its minimum energy conformer has been obtained for N-(2-(Trifluoromethyl)phenyl)acetamide. Fourier Transform Infrared and Fourier Transform Raman investigation have been done experimentally and theoretically. Nuclear Magnetic Resonance analysis has been performed to obtain 1H and 1C chemical shifts. Ultraviolet-Visible analysis has been performed to obtain maximum absorption wavelength. The molecular orbital diagram with different energies has been obtained and compared with the band gap of Ultraviolet-Visible data. Wave function analysis has been discussed to know the electronic properties. Thus, this present study reports the structural, electrical, chemical activities of the title compound. [ABSTRACT FROM AUTHOR]

Three lanthanide complexes (La(III), Er(III), and Yb(III)) derived from ferrocene-based Schiff base ligand (HL) were synthesized from condensation of 2-aminophenol with 2-acetylferrocene. The ligand and metal complexes were characterized based on elemental analyses, IR, 1H NMR, molar conductance, SEM and thermal analyses (TG, DTG). The molar conductance revealed that all the metal chelates were electrolytes having the general composition [M(L)(Cl)(H2O)3]Cl·4H2O. HL and its complexes were screened for their antibacterial and antifungal activity by agar diffusion method. The results of these studies showed that the metal complexes are more effective antibacterial and antifungal agents as compared with the free ligand. The anticancer activity was screened against human breast cancer cell line (MCF-7). Results indicated that metal complexes showed an increased cytotoxicity in proliferation to cell lines as compared to free ligand. Molecular docking studies were performed to identify the binding orientation or conformation of a complex in the active site of the protein. HL and its complexes were docked with crystal structure of DDB1 of breast cancer, crystal structure of HCV, RNA-dependent RNA polymerase, receptors of HBV core protein, crystal structure of the Fab fragment of anti-HAV. [ABSTRACT FROM AUTHOR]

Photochromic diarylethene oxime isomers were obtained by coupling between hydroxylamine hydrochloride and 2,3-bis(2,5-dimethylthiophene-3-yl)thiophene-5-carbaldehyde. The two isomers were confirmed by NMR. Photochromic behavior was investigated in THF. Reversible photochromism could be induced by alternated UV/Visible light. The solution color also can be toggled between colorless and light purple. Corresponding photo- and thermo-stability measurements indicate that they are stable in the dark at room temperature. However, the degradation of the two isomers is accelerated with the temperature rising and prolonged exposure to UV light. Optimized geometry structure and frontier molecular orbitals further supported their photochromic activity. [ABSTRACT FROM PUBLISHER]

Pyrazolines derivatives are nitrogen-containing heterocyclic compound, which exhibit the broad spectrum of biological activities such as antibacterial, antifungal, antiprotozoal, and anti-inflammatory. The optimized geometry, frequency, and intensity of vibrational bands of these compounds are obtained by the density function theory (DFT) using 6–31+G(d,p) basis set. The scaled harmonic vibrational frequencies have been compared with experimental Fourier transform infrared spectroscopy (FTIR) values and found to be in good agreement. The electronic properties of these molecules are discussed with the help of highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and molecular electrostatic potential (MESP) surfaces, and a number of electronic and thermodynamic parameters are calculated, which are closely related to their chemical reactivity and reaction path. We also notice that pyrazoline derivatives show biological activity for preventing dyskinesia. This study may provide a further investigation on pyrazolines derivatives for pharmacological importance. [ABSTRACT FROM AUTHOR]

With the enumeration of the triangular lattice fragments, we have systematically investigated the graphene clusters (CnHm, n = 14 – 24) with various sizes and shapes, whose structural stabilities and electronic properties are studied by the Hückel molecular orbital (HMO) method and the first-principles calculation. According to the formation energies, we show the structural stabilities of the clusters are closely related to the shape and size, as well as the chemical potential of hydrogen. The energy gaps obtained from the HMO method are in the same trend with the ones calculated by the first-principles calculations, indicating the effective screening of the gap minimum and maximum in a fast speed. There is a general decreasing of the energy gaps with the size increment due to the quantum confinement, meanwhile, the gaps are also highly dependent on the shape of the clusters for those with the same number of carbon atom. [ABSTRACT FROM PUBLISHER]

This study deals with the identification of glutamic acid by means of quantum chemical approach. FT-IR, FT-Raman and UV–vis spectra were recorded in the region 4000–400, 4000–50 cm− 1and 200–600 nm, respectively. CAM-B3LYP/6-31G(d,p) and B2PLYP/6-31G(d,p) calculations were performed to obtain the optimised molecular structures, vibrational frequencies and corresponding vibrational assignment, thermodynamic properties and natural bonding orbital (NBO) analysis. The results show that the obtained optimised geometric parameters (bond lengths, bond angles and bond dihedrals) and vibrational frequencies were found to be in good agreement with the experimental results. The calculations of the electronic spectra were compared with the experimental ones. Furthermore, highest occupied molecular orbital and lowest unoccupied molecular orbital analyses and UV–vis spectral analysis were also performed to determine the energy band gaps and transition states. NBO analysis, calculated using density functional theory methods (CAM-B3LYP/6-31G(d,p) and B2PLYP/6-31G(d,p)), was induced to find inter-molecular atoms.13C and1H NMR isotropic chemical shifts were calculated and the assignments made were compared with the ChemDraw Ultra values. [ABSTRACT FROM AUTHOR]

In this study, anodic oxidation potentials of a training set of the selected 14 β-diketones and β-diketoesters were measured by means of cyclic voltammetry on a glassy carbon electrode and correlated with the highest occupied molecular orbital (HOMO) calculated at the #B3LYP/6-311+G** level. HOMO energy level and HOMO structural map were used to make a powerful model to classify molecules which show similar chemical and electrochemical behaviours. The linear correlation between anodic peak potential,EpA, andEHOMOof classified compounds, certifies that they have the same mechanism of the electron transfer reaction. [ABSTRACT FROM AUTHOR]

We present a size-extensive extension to the CC2 model that avoids the complications with quasi-degeneracies that are present in the CC2 model and related perturbation theory-based approaches. The formulation also provides a consistent model for treating different parts of a molecular system at different levels of electron correlation. Such a subsystem approach leads to large reductions in the computational requirements without compromising the accuracy. In this initial study, we focus on static molecular properties. [ABSTRACT FROM AUTHOR]

The solvent structure and binding motif of iodide-doped tetrahydrofuran clusters, I−(THF) n (1 ≤ n ≤ 30) are investigated with anion photoelectron imaging, molecular dynamics simulations, and ab initio calculations of vertical detachment energies. Experimentally, a dramatic decrease in the iodide differential stabilization energy and concomitant change in the mass spectrum at n = 9 suggest that the first solvation shell closes at n = 9–10 THF molecules, in rough agreement with the theoretical result of n = 7–9 determined from the computation of relaxed and unrelaxed solvent distribution densities. Analysis of the vertical detachment energy vs. inverse cluster radius suggests the iodide atom is maximally coordinated around n = 9. Decomposition of the interaction energies of I−(THF), its vertically-detached complement, and the (THF)2 dimer, employing the absolutely-localized molecular orbital energy decomposition analysis (ALMO EDA) scheme, highlights the dependence of electron binding and detachment on both electrostatics and polarization, with direct evidence of the fundamental importance of polarizability to a description of detachment. Experimental and theoretical evidence for an anionic electronically excited state is also presented; computed excitation energies and their attendant characters are discussed. The results are interpreted within the framework of the inefficient packing that occurs in bulk neat THF. [ABSTRACT FROM AUTHOR]

The geometrical structures, relative stabilities, and electronic properties of pure and Cs2-doped gold clusters have been determined by employing the density functional method with the relativistic effective core potential. The results show that doping with two Cs atoms dramatically affects the geometries of the ground-state pure gold clusters and the doped Cs atoms prefer to locate at the symmetry position. The relative stability of these clusters is examined via analysis of the averaged atomic binding energies, fragmentation energies, the second-order difference of energies and the highest occupied–lowest unoccupied molecular orbital energy gaps as a function of cluster size. The results exhibit a dramatic even–odd alternative behavior. In particular, it should be noted that a maximum peak is observed for Cs2Au n clusters at n = 2, implying that the Cs2Au2 cluster possesses relatively higher stability. In addition, the charge transfers, VIPs, VEAs, chemical hardnesses and polarizabilities have been analysed and compared. [ABSTRACT FROM PUBLISHER]

In this (first) paper we attempt to generalize the notion of tensor connectivity, subsequently studying how this property is affected in different tensorial operations. We show that the often implied corollary of the linked diagram theorem, namely individual size-extensivity of arbitrary connected closed diagrams, can be violated in Coulomb systems. In particular, the assumption of the existence of localized Hartree–Fock orbitals is generally incompatible with the individual size-extensivity of connected closed diagrams when the interaction tensor is generated by the true two-body part of the electronic Hamiltonian. Thus, in general, size-extensivity of a many-body method may originate in specific cancellations of super-extensive quantities, breaking the convenient one-to-one correspondence between the connectivity of arbitrary many-body equations and the size-extensivity of the expectation values evaluated by those equations (for example, when certain diagrams are discarded from the method). Nevertheless, assuming that many-body equations are evaluated for a stable many-particle system, it is possible to introduce a workaround, called the ε-approximation, which restores the individual size-extensivity of an arbitrary connected closed diagram, without qualitatively affecting the asymptotic behavior of the computed expectation values. No assumptions concerning the periodicity of the system and its strict electrical neutrality are made. [ABSTRACT FROM PUBLISHER]

The mutagenic activity of nitrated pyrenes (NPs) depends largely on the number and the position of the nitro group. To elucidate the differences in the mutagenicity, we performed molecular orbital calculations for seven NPs, their metabolic intermediates, and their DNA adducts. The extension of the investigation to the metabolites provided no significant improvement. The heats of formation, however, of NP-DNA adducts were correlated with the mutagenicity; the DNA model was composed of five base pairs with the sequence of guanine-thymine-guanine-guanine-guanine and nitrenium ions of NPs as an ultimate mutagen were bonded at the C8 position of the middle guanine. A plot of the heats of formation against the logarithms of the mutagenic activity showed a good linearity with a correlation coefficient of −0.85. The results suggest that the stability of the NP-DNA is an important factor to determine the mutagenicity of NPs. [ABSTRACT FROM PUBLISHER]

The impacts of the generalized anomeric effect (GAE) and gauche effect (GE) associated with donor–acceptor electron delocalizations and dipole–dipole interactions on the conformational properties of 2-methoxy- (1), 2-methylthio- (2), 2-methylseleno- (3), 2-fluoro- (4), 2-chloro- (5), and 2-bromocyclohexanone oxime (6) have been studied by means of hybrid density functional theory (B3LYP/6–311+G**) and ab initio molecular orbital (HF/6–311+G**)-based methods and natural bond orbital (NBO) interpretation. Both methods used showed that the above compounds exist predominantly in the axial chair conformation and the axial conformation stability increased from 2-methoxy- (1) to 2-methylselenocyclohexanone oxime (3) and also from 2-fluoro- (4) to 2-bromocyclohexanone oxime (6). The NBO analysis showed that the GAE increases from compound 1 to compound 3 and also from compound 4 to compound 6. GE does not have significant impact on the conformational behaviors of compounds 1–6 and GAE succeeds in accounting qualitatively for the increase of the axial preferences in both series of compounds. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Table S1. Supporting Information Available. The structures optimized and thermodynamic functions of the axial and equatorial conformations of compounds 1–6. This material is available free of charge via the Internet. GRAPHICAL ABSTRACT [ABSTRACT FROM AUTHOR]

Molecular structure, atomic charges, dipole moments, total energies, and vibrational frequencies of 4-(benzhydryloxy)phthalonitrile in the ground state have been calculated using density functional theory (DFT) calculations and compared with the experimental data. Calculated frequencies are in good agreement with the corresponding experimental data. To determine conformational flexibility, the molecular energy profile of the title compound was obtained by semi-empirical (RAM1) calculations with respect to the selected torsion angle, which was varied from -180° to +180° in steps of 10°. In addition, frontier molecular orbitals (FMOs) analysis and thermodynamic properties of the title compound were investigated using theoretical calculations. [ABSTRACT FROM AUTHOR]

The geometric structures, relative stabilities, and electronic properties of a series of tetra-aluminum oxide clusters, [image omitted] ( [image omitted], [image omitted]), were systematically investigated using density functional theory calculations at the B3LYP level. The optimized geometries reveal a structural transition from a two-dimensional to a three-dimensional structure for n ≤5 for the neutral species, but the three-dimensional structures are preferable for all negative clusters with the exception of [image omitted]. The dissociation energy, the second difference energy and the highest occupied-lowest unoccupied molecular orbital gaps as a function of the cluster size exhibit a significant even-odd alternation phenomenon. It is found that the neutral [image omitted] cluster is relatively stable and exhibits strong chemical stability. Furthermore, the calculated (vertical and adiabatic) electron detachment energies are also compared with previous experimental data obtained from photoelectron spectra. [ABSTRACT FROM AUTHOR]

The molecular rotation parameters of cholesteric liquid crystals (LCs) are calculated based on their phase transition temperatures using a semi-empirical molecular orbital method. A molecular rotation model is employed to evaluate the correlation between the LC phase transition and their molecular structure. The cholesteric-isotropic phase transition temperature and critical rotational velocity are regularly reduced with increasing molecular length. A novel explanation for the molecular interaction effect on phase transition is proposed. For low-temperature phases, the molecular interaction is strong and plays a key role in the phase transition. In contrast, for high-temperature phases, the molecular rotation effect becomes the important factor for the phase transition. [ABSTRACT FROM AUTHOR]

Large condensed polycyclic aromatic hydrocarbons (LCPAHs) generally have distorted structures due to steric repulsion between neighboring hydrogen atoms. The distortion may influence their physicochemical properties such as electric conductivity, photoconductivity, and photochromism. Accordingly we have synthesized LCPAHs and analyzed their structure. In the present study, we synthesized an undecacyclic aromatic compound, dibenzo[a,rst]-dinaphtho[2,1,8-klm:1',2'-o]pentaphene (DDPP) and determined the structure by use of NMR spectroscopy. To assign the 1H- and 13C-NMR chemical shifts completely, we used the HMQC-TOCSY (Heteronuclear Multiple Quantum Coherence-Total Correlation SpectroscopY) method in which the original proton-carbon correlation is relayed to neighboring protons in the same spin-system. Furthermore, we compared the chemical shifts (δs) of the heptacyclic aromatic hydrocarbon, peropyrene, the nonacyclic, violanthrene B (VEB), and the undecacyclic, DDPP, and investigated correlations between their local structure and δs. For the protons in the bay region, the averaged δs decrease as molecular size increases: 9.23 ppm (hepta-) > 9.07 ppm (nona-) > 8.77 ppm (undeca-). Similar change in the δs is also found for the protons in the cove region: 9.37 ppm (nona-) > 8.81 ppm (undeca-). Thus, it is noted that the averaged δs for the protons in the cove region become downfield than those for the protons in the bay region. The findings are explained in terms of the anisotropic effect of the local magnetic field of benzene rings. [ABSTRACT FROM AUTHOR]

The ring carbo-mer of silole, termed as carbo-silole, was investigated at the DFT level of theory (B3PW91/6-31G**) and compared to its carbo-cyclopentadiene and carbo-cyclopentadienone analogues. The electronic delocalization of these species and their parent molecules is analyzed indirectly from their optimized geometry, and directly from their canonical and NBO molecular orbitals by comparison of the HOMO-LUMO gaps. All criteria indicate that the π electron systems of carbo-silole and carbo-cyclopentadiene are delocalized to a similar extent, in particular through a π - σ*AH2 conjugation (A = C, Si). The cyclic component of the delocalization, i.e., aromaticity, has been more directly appraised by calculation of NICS values at the center of the rings: the latter definitely confirm that in contrast to carbo-cyclopentadienone (NICS = -8.1 ppm), both carbo-silole (NICS = -1.1 ppm) and carbo-cyclopentadiene (NICS = +2.4 ppm) are non-aromatic. The electron affinity is significantly increased by carbo-merization of silole (from 0.25 to 1.95 eV), suggesting that the carbo-silole ring might be a relevant unit for the design of functional materials. Studies of the carbo-silolylium cation show that its aromaticity is comparable to that of the long studied carbo-cyclopentadienyl analogue. [ABSTRACT FROM AUTHOR]

The geometrical parameters, vibrational frequencies, and dissociation energies for (H2O)n and C6H6(H2O)n (n = 1-7) clusters have been investigated using density functional theory (DFT) with various basis sets. The highest levels of theory employed are B3LYP/aug-cc-pVTZ for optimization and MP2/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ for binding energy. The harmonic vibrational frequencies and IR intensities are also determined at the various levels of theory to confirm whether the hydrogen-bonded structure of water complex (Wn, n = 1-7) is affected by the presence of benzene. The effect of benzene on the OH stretch modes of benzene-water complex (BWn, n = 1-7) is observed in the π-hydrogen bonded OH stretch. For each of the BWn clusters the intensity of this mode is increased significantly due to charge transfer/polarization interactions and the frequency shifts from Wn to BWn are in the range of 40-60 cm-1. The calculations give the binding energies of 2.58, 4.20, 3.27, 3.00, 3.42, 4.14, and 5.49 kcal/mol for BW1-BW7, respectively after ZPVE and 50%-BSSE corrections. [ABSTRACT FROM AUTHOR]

Analytical energy gradients have been implemented in the DALTON program at the level of explicitly correlated second-order Møller-Plesset perturbation theory (MP2-R12). The implementation has been accomplished for standard approximation A using an auxiliary basis which is the same as the orbital basis for the resolution-of-the-identity, with and without frozen core. As a test calculation, the geometries of nine stationary points on the potential energy surface of the water dimer have been optimized and the results are compared with earlier studies. [ABSTRACT FROM AUTHOR]

A mathematical analysis of several algorithms, for the integration of the differential equation associated to the Intrinsic Reaction Coordinate path, is performed. This analysis first shows that the Intrinsic Reaction Coordinate path can be derived from a variational problem, so that it has the properties of an extremal curve. Then, one may borrow the mathematical methods for the integration of extremal curves, to formulate new algorithms for the integration of the Intrinsic Reaction Coordinate path. One may use also this theoretical framework, to recast recently formulated algorithms based on direct minimization of an arbitrary curve, such as the Nudged Elastic Band Method or String Method. In this view a new algorithm is proposed. Finally, the theory of broken extremals is used to analyse an Intrinsic Reaction Coordinate path possessing a valley ridge inflection point. [ABSTRACT FROM AUTHOR]

Scaling factors have been derived to obtain fundamental vibrational frequencies with the recently introduced semiempirical molecular orbital methods RM1 and PM6, implemented in MOPAC2007. A least-squares approach is used with a training set comprised of 90 singlet-state molecules and 922 distinct vibrations, extracted from the NIST Computational Chemistry Comparison and Benchmark Database (CCCBDB). Results are presented both for the conventional Scott-Radom type single-factor fitting, and for a multi-factor linear model: Semiempirical Semiglobal Self-consistently Scaled Quantum Mechanical (S4QM). The new NDDO methods in conjunction with the multi-linear fitting are shown to yield improved prediction of vibrational frequencies. To demonstrate the performance of S4QM//PM6 for calculating vibrational spectra, the examples of indene, indazole and four tetrachlorinated p-dibenzodioxins are presented. [ABSTRACT FROM AUTHOR]

The high-accuracy W4 computational thermochemistry protocol, and several post-W4 methods, have been applied to the P2 and P4 molecules. Contrary to previous studies, we find the experimental thermochemistry to be fundamentally sound. The reaction enthalpy for P4→2P2 has a very significant contribution from post-CCSD(T) correlation effects. We derive a gas-phase heat of formation for the phosphorus atom of [image omitted] kcal mol-1 and [image omitted] kcal mol-1, in the upper half of the CODATA uncertainty interval. [ABSTRACT FROM AUTHOR]

We calculated the variational and diffusion quantum Monte Carlo forces using the Hellmann-Feynman theorem and Pulay's correction for the first-row diatomic and triatomic molecules (CO, NO, CO2 and NO2). It is demonstrated that Pulay's correction is important for accurate calculation of forces on non-hydrogen atoms. [ABSTRACT FROM AUTHOR]

A computer program has been written to perform analytic derivative calculations of magnetic response properties based on uncontracted multireference configuration interaction (MRCI) wavefunctions. At this point, orbital relaxation is neglected in this treatment and the basis functions are assumed to be independent of the perturbation. It is therefore equivalent to an untruncated sum-over-states (SOS) approach to the g-tensor. Hence, the treatment is more rigorous than all previous MRCI g-tensor calculations that have used truncated SOS formulations. In the present calculations, MRCI calculations were performed on top of full valence complete-active space self-consistent field (CASSCF) reference wavefunctions without truncation of the reference or correlation spaces. Results are reported for two types of spin-orbit coupling operators, a simple effective nuclear charge approximation and the spin-orbit mean field (SOMF) approximation. The effects of orbital relaxation are discussed. The values obtained can be used in future calibration studies. [ABSTRACT FROM AUTHOR]

An implementation of the projected gradient method for locating the minimum energy crossing point between electronic states of different symmetry/multiplicity within the equation-of-motion coupled-cluster family of methods is reported. The method is applied to characterize the intersections between electronic states in [image omitted], NO2, and para-benzyne using the excitation energies, ionization potential, and spin-flip variants of the equation-of-motion coupled-cluster methods. The performance of the algorithm is discussed and recommendations for improving the convergence in problematic situations are given. [ABSTRACT FROM AUTHOR]

An IC-MRCI ansatz has been used in conjunction with augmented quadruple-ζ basis sets to construct an 89-point potential energy surface of the ground electronic state of [image omitted]. The equilibrium structure was predicted to be of C2v symmetry, possessing Be-H bond lengths of 1.609 Å and a H-Be-H bond angle of 29.4°. A rational Padé analytical function was fitted to the discrete IC-MRCI grid yielding a [image omitted] value of 5.20 cm-1. It was embedded in the t-coordinate Eckart-Watson Hamiltonian to calculate vibrational and rovibrational wave functions. For the vibrational ground state, the vibration-averaged bond lengths and angle were 1.647 Å and 29.2°, respectively. An embedded analytical IC-MRCI dipole moment function fitted to 73 discrete points was transformed to the space-fixed frame. Rovibrational radiative properties were calculated using this surface in conjunction with a novel integration scheme. [ABSTRACT FROM AUTHOR]

Conformational studies were carried out on acetylcholine and two nerve agents (NAs), soman and sarin, to determine the influence of the low-energy conformers of NAs in inhibiting the hydrolysis of acetylcholine using state-of-the-art quantum chemical techniques. Different enantiomers of sarin and soman were taken into account during the conformational analyses. The aqueous solvation of these molecules was studied at the density functional level using the polarized continuum model with the conductor-like reaction field approach. The results show that, compared with acetylcholine, the NAs have less conformational flexibility in the gas phase. The conformational flexibility of these molecules increases during aqueous solvation, and the transition barrier to different low-energy conformations also decreases. This property, together with the molecular electrostatic potential surfaces of the NAs, was compared with those of acetylcholine to obtain an insight into the cholinesterase inhibition properties of these molecules. [ABSTRACT FROM AUTHOR]

The reaction pathways to [image omitted] (tolyl, benzyl, and tropylium) from o-, m-, and p-chlorotoluene radical cations have been studied at the SCF level of theory using the DZ and DZP basis sets. The equilibrium structures and relative energies for the local minima and transition states have been fully optimized and the harmonic vibrational frequencies have been evaluated to differentiate the local minimum and the transition state. The lowest barrier rearrangement pathway is the formation of the benzyl cation for all three isomers, corroborating the recent experimental findings of Kim and Shin. This benzyl channel involves [1,3] α-hydrogen migration at the entrance and the activation energy is calculated to be 40.3, 39.7, and 42.2 kcal mol-1 for the o-, m-, and p-isomer, respectively. The other competing rearrangement pathway involves [1,2] α-hydrogen migration at the entrance, which leads to the tropylium ion, and the activation barrier is predicted to be 55.5, 54.2, and 56.62 kcal mol-1 for the o-, m-, and p-isomer, respectively. The highest barrier process involves direct C-Cl bond cleavage that yields the tolyl cation with a 0 K dissociation energy of 61.6, 64.6, and 68.92 kcal mol-1 for the o-, m-, and p-isomer, respectively. [ABSTRACT FROM AUTHOR]

A hydroiodic acid molecule is dissociated by more than four water molecules. Here, the effect of an excess electron on the hexahydated hydroiodic acid where the dissociated structure [H3O+(H2O)5I-] is much more stable than the undissociated one [(H2O)6HI], is investigated. Upon binding an excess electron (e-), the cluster releases a hydrogen radical and forms the stable hexahydrated iodide [(H2O)6I-] when the initial kinetic energy is above ∼200 K, due to the small transition barrier (∼0.5 eV). The system with the hydrogen radical released, [(H2O)6I- + H·], is much more stable than the systems with an excess electron, [(H3O)+{e-(H2O)5}I-] or [e-(H2O)2(H3O)+(H2O)3I-]. [ABSTRACT FROM AUTHOR]

Coupled cluster and density-functional theory calculations of the electronic circular dichroism (ECD) spectra and optical rotatory dispersion (ORD) of (S)-methyloxirane and (S)-methylthiirane have been carried out for comparison to gas-phase experimental data. Coupled cluster simulations of the ECD spectra of both molecules are in excellent agreement with experiment, both for the positions of the transitions and for the signs and magnitudes of the rotational strengths. Density-functional theory yields the correct structure of the ECD spectra, but the transition energies are shifted to lower energies by up to 0.3 eV. Density-functional ORD curves of (S)-methylthiirane exhibit incorrect dispersion due to an early onset of the Cotton pole. The coupled cluster ORD curves of (S)-methylthiirane give the correct sign of the rotations, but overestimate their magnitude by up to 50% at shorter wavelengths. Although temperature-dependent harmonic vibrational corrections improve the comparison between coupled-cluster theory and experiment at 633 nm, such corrections produce an incorrect sign of the rotation at 355 nm. [ABSTRACT FROM AUTHOR]

We investigate isotope effects in dihydrogen systems using the nuclear orbital plus molecular orbital (NOMO) theory, which simultaneously determines nuclear and electronic wave functions without the Born-Oppenheimer approximation. In order to estimate the vibrational averaging bond distances, the analytical energy gradients are used for the NOMO theory. The bond distances of three dihydrogen-bonded systems, namely H3NX+ ··· XBeH, LiX ··· XC2H and H2BX ··· XF for X = H, D and T, are obtained. The X ··· X bond distances decrease with respect to the substitution T → D → H, which is contrary to the behaviour of typical hydrogen bonds. This indicates that isotope effects strengthen the X ··· X bond. This behaviour is analogous to the Ubbelohde effect observed in the solid phase. [ABSTRACT FROM AUTHOR]

Analytic energy gradients with respect to atomic coordinates for systems with translational invariance are formulated within the framework of Kohn-Sham Density Functional Theory. The energy gradients are implemented in the BAND program for periodic DFT calculations which directly employs a Bloch basis set made up of Slater-type (STOs) and numeric atomic orbitals (NAOs). The details of our implementation are described including the use of symmetry in the reciprocal and direct spaces, as well as the application of the frozen core approximation. [ABSTRACT FROM AUTHOR]

We present simple CAS-DFT approaches for degenerate and nearly degenerate systems. In this method, we do not employ any auxiliary variables, but employ the effective CASCI-DFT and CASSCF-DFT equations for the ground and excited states. Simple applications for fundamental systems such as atomic multiplet states (C, N+n, and O+n), the transition metal complex V(III)L6 (L = H2O and CO) and the Cu(II) acetate dimer Cu(II)2(Ac)4(H2O)2 are presented. The results are discussed from the viewpoint of the shapes of the potential curves of several nearly degenerate spin states, the theory of molecular magnetism and the reliability of the CAS space employed. The computational results are fully compatible with the experimental results available, and also with those of ligand field theory. [ABSTRACT FROM AUTHOR]

The reaction force F(R) of a chemical or physical process is the negative derivative of the system's potential energy V(R) along the reaction coordinate. The features of F(R) - its maxima, minima and zeroes - divide the process into well-defined stages which can, in general, be characterized in terms of changes in structural and/or electronic properties. This has been demonstrated for bond dissociation/formation and for reactions that have activation barriers in both forward and reverse directions. An important aspect of the reaction force is that it naturally and unambiguously divides activation energies into two components, one corresponding to the preparative structural stage of the process and the other to the first phase of the transition to products. It is shown how this can help to elucidate the effect of a solvent or a catalyst upon an activation barrier. [ABSTRACT FROM AUTHOR]

The traditional formulation of a molecular wave function describing the motion of the electrons and the nuclei in terms of the Born hierarchy does not allow us to account for the participation of the electrons in vibrational or rotational motion, except by resorting to a fully non-adiabatic treatment, abandoning completely the concept of a single potential energy surface for one electronic state of the molecule. An alternative approach is presented that is based on an exact separation in all possible dissociation limits. One obtains a wave function of a generalized valence bond form in terms of neutral fragments with the adiabatic ansatz in the limit of infinite nuclear masses. An energy expression is obtained correct to O(M-2), where M is a representative nuclear mass in units of the electron mass. This expression involves a single potential energy surface, but a geometry-dependent reduced mass for vibration and rotation, in which the participation of the electrons is taken care of. The vibrational mass differs from the rotational mass. For [image omitted] and H2, approximations to these effective masses are obtained for the first time in a simple way in terms of a LCAO or a Heitler-London formalism, respectively. In [image omitted] the electron participates to roughly 60% in vibration, but only about 30% in rotation. Similar values are found for H2. Such a fractional participation appears typical for valence electrons, whereas inner-shell electrons are likely to participate fully both in vibration and rotation. [ABSTRACT FROM AUTHOR]

The coupled-cluster singles and doubles treatment with a perturbative treatment of triple excitations known as CCSD(T) has been used in conjunction with a hierarchy of atomic natural orbital basis sets to study stretching levels in water up to 2 eV above the zero-point level. Agreement with experiment obtained with perturbation theory augmented by a simple treatment of resonances suggested by Lehmann is quite remarkable in spite of the well-known and strong Darling-Dennison resonances in this system. With the largest basis sets, deviation from experiment is ca. 20 cm-1 at energies in the 15,000-16,000 cm-1 range. [ABSTRACT FROM AUTHOR]