Density Functional Theory Level Calculations Research Articles

A chitosan N‐ium acetate catalyzed Michael‐aldol‐dehydration‐imino‐Diels‐Alder reaction: One‐pot synthesis of new angular acridine‐fused heterocycles

AbstractA highly efficient domino protocol, Michael‐aldol‐dehydration‐imino‐Diels‐Alder (MAD‐IDA) reaction, that allows the intermediate MAD to combine effectively with the arylamine released from the slow reduction of nitroarene via IDA reaction has been described and several new V‐shaped acridine‐heterocycles have been synthesized after stirring 2‐mercapto‐quinoline‐carbaldehydes/2‐mercapto‐pyridine carbaldehyde/2‐hydroxy‐naphthaldehyde, citral/croton‐aldehyde, and NaSH in chitosan N‐ium acetate in aqueous ethanol at room temperature. The stereo and regioselectivities of the reaction were confirmed by the 2D NMR experiment and the density functional theory level calculations.

The influence of molecular flexibility on the mesogenic behavior of a new homologous series based on azo-azomethine: Synthesis, characterization, photoisomerization and DFT study

Through condensation of 2-hydroxy-4-n-alkoxybenzaldehyde (n = 2 to 8, 10, 12, 14, 16, 18) with (E)-4-((2,4-dimethylphenyl)diazenyl) benzene-1,3-diamine, new homologous series of rod shaped calamite liquid crystals based on azo-azomethine have been prepared. All synthesized compounds were characterized by FT-IR, 1H NMR, and 13C NMR spectroscopy. Use Differential Scanning Calorimeter (DSC) and Polarizing Optical Microscope (POM) to check the liquid crystal properties of all synthetic compounds. In the homologous series, all the compounds are mesogenic; some of them are in the nematic phase; some of them appear in the smectic A phase, and some appear in the nematic and smectic A phases. UV–vis pectroscopy was used to study the photoisomerization in chloroform. DFT (Density functional theory) level calculations and complete geometric optimization of all synthetic compounds are performed using B3LYP/6-31+G (d, p) basis sets.

New insights into the vibrational spectroscopic investigation on S-cis & S-trans forms of 2-Methoxy benzoyl chloride

The conformal stability of 2-Methoxy benzoyl chloride (2MBC) in its S-cis and S-trans forms was investigated using Density Functional Theory (DFT) calculations and Potential energy surface scan analysis. The experimental (FT-IR and FT-Raman) spectra were recorded in the condensed phase in order to perform detailed vibrational analysis. Different basis sets were adopted during optimization procedure and the suitable method was identified from the results obtained. The optimized geometry and vibrational wavenumbers were determined by using B3P86/6-31++G(d,p) level Density Functional Theory calculations and was found to be the most suitable one. The effect of scaling on the calculated wavenumbers was analyzed by employing unscaled, uniform scaling and selective scaling procedures. A detailed comparative analysis of the effect of hydrogen bonding on the geometry and structural parameters of both the conformers has been carried out using the results obtained from DFT level calculations. The results from the above studies reveal that, the presence of intramolecular hydrogen bond in S-cis conformer of 2MBC has significantly altered the geometrical parameters and hence the vibrational wavenumbers. The difference in electron transfer mechanism of the two different environments (S-cis and S-trans) was thoroughly investigated using Natural Bond Orbital analysis.

New insights into the conformal stability, influence of hydrogen bonding and vibrational analysis of 2,6- and 3,5-Dihydroxyacetophenone – A comparative study

The conformal stability of 2,6-Dihydroxyacetophenone (DHAP I) and 3,5-Dihydroxyacetophenone (DHAP II) were investigated using Potential Energy Surface scan studies and B3LYP/6-31G** level Density Functional Theory(DFT) calculations. The experimental (FT-IR and FT-Raman) spectra were recorded in the condensed phase in order to perform detailed vibrational analysis. The optimized geometry and vibrational wavenumbers were determined by using B3LYP/6-31G** level Density Functional Theory calculations. The effect of scaling on the calculated wavenumbers was analyzed by employing unscaled, uniform scaling and selective scaling procedures. A detailed comparative analysis on the effect of hydrogen bonding on the geometry, structural parameters and vibrational wavenumbers has been carried out using the results obtained from PES scan and DFT level calculations. The results from the above studies reveals that, the presence of strong intramolecular hydrogen bond in DHAP I has significantly altered the geometrical parameters and hence the vibrational wavenumbers. The hydrogen bonding in DHAP I is strong enough to make it more stable compared to that of DHAP II.

Hydrophosphination of Carbodiimides Using Protic Heptaphosphide Cages: A Unique Effect of the Bimodal Activity of Protonated Group 15 Zintl Ions

Direct reaction of the hydrogen heptaphosphide dianion, [HP7]2– (1), with carbodiimides RN═C═NR (R = Dipp (2,6-diisopropylphenyl), iPr, Cy) afforded the amidine-functionalized Zintl ions [P7C(NHR)(NR)]2– (R = Dipp (2), iPr (3), and Cy (4)). The bimodal activity of 1, which contains both negatively charged phosphide vertices alongside “electron-precise” phosphine-like nuclei allows for the direct hydrophosphination of the carbodiimides without need for an external proton source. Further reaction of the bis(2,6-diisopropylphenyl)amidine-functionalized cluster 2 with a proton source such as [NH4][BPh4] or [H(OEt2)2][BArF4] affords the protonated monoanionic species [HP7C(NHDipp)(NDipp)]− (5). As with 1, species 5 also has bimodal character, and additional hydrophosphination reactions are possible by reacting 5 with RN═C═NR to yield the bis-functionalized monoanions {[P7[C(NHDipp)(NDipp)][C(NHR)(NR)]}− (R = Dipp (6), iPr (7), and Cy (8)). All species were characterized by multielement NMR spectroscopy and electrospray mass spectrometry. In addition clusters 3, 5, and 6–8 were characterized by single-crystal X-ray diffraction in [K(18-crown-6)]2[3], [K(2,2,2-crypt)][5], [K(2,2,2-crypt)][6]·THF, [K(2,2,2-crypt)][7]·hex, and [K(2,2,2-crypt)][8]·0.65THF·0.35hex, respectively. Density functional theory level calculations were conducted on all anionic species to probe their electronic structure.

Synthesis, structures, photoluminescence, and theoretical investigations on two new Zn(II)/Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands

Two new neutral mononuclear Zn(II) and Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands, [Zn(paH)2(OAc)2]·2CH3OH (paH = pyridine-2-amidoxine, HOAc = acetic acid) (1), and [Mn(paH)2(OAc)2]·C2H5OH·2H2O (2), have been prepared and characterized structurally by X-ray crystallography. 1 and free paH exhibit photoluminescence at room temperature in solid state, which is rare so fare for metal complexes with oxime-based ligand. The emissions of 1 and free paH arise from the metal-perturbed paH-based π → π* ligand-to-ligand charge transfer transition (LLCT) and π → π* charge transfer transition in nature, respectively, in terms of the density functional theory level calculations and molecular orbital analyses. Two new neutral mononuclear Zn (II) and Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands, [Zn(paH)2(OAc)2]·2CH3OH (paH = pyridine-2-amidoxine, HOAc = acetic acid) (1), and [Mn(paH)2(OAc)2]·C2H5OH·2H2O (2), have been synthesized and characterized structurally. The rarely reported photoluminescent behavior for oxime-based metal complexes has been observed in solid 1, indicating that such neutral mononuclear oxime-based metal complexes are a new class of potential candidates for photoluminescence and/or electroluminescence devices. The photoluminescent property and spectroscopic shifts have been investigated in detail for 1 and free paH ligand by means of the density functional theory level calculations and molecular orbital analyses. The emission for 1 and free paH ligand, are related to the metal-perturbed paH-based π → π* ligand-to-ligand charge transfer transition (LLCT) and π → π* charge transfer transition in nature, respectively.

O1s photoionization dynamics in oriented NO2

We have performed extensive density functional theory (DFT) calculations, partial cross sections, dipole prepared continuum orbitals, dipole amplitudes and phase shifts, asymmetry parameters β, and molecular frame photoelectron angular distributions, to elucidate the O1s photoionization dynamics of NO(2) molecule with emphasis on the shape resonances in the O1s ionization continuum. In the shape resonance region, the β parameters and photoelectron angular distributions have been compared with our experimental results. Fairly good agreement between the theory and experiment has confirmed that the DFT level calculations can well describe the photoionization dynamics of the simple molecule such as NO(2). Interference due to equivalent atom photoionization is theoretically considered, and the possibility of detection of the effect in the two degenerate channels with different combinations of light polarization and photoemission direction is discussed.

A Computational Study of the Kinetics and Mechanism of the Gas Phase Pyrolysis of Allyl Methyl Amine

A density functional theory (DFT) study has been carried out at the B3LYP/6-31G(d) level on the gas-phase retro-ene reaction of allyl methyl amine (AMN). The results were compared with single point calculations at a high level of the theory, using the G3MP2 method. Two mechanisms for this kind of reaction are possible, one involves a six-membered cyclic transition state (TS) and the other is a multistep, free radical mechanism. Both DFT and high level calculations show that propene and imine formation are in accordance with a concerted cyclic mechanism. Natural bond orbital analysis (NBO) and atoms-in-molecule (AIM) procedures show that the reaction achieves a synchronicity value of 90%. The calculated kinetic parameters for AMN pyrolysis agree with the available experimental results.

A combined experimental and theoretical approach to the study of methane activation over oxide catalysts

We present new results on the activation of methane over pure and doped gallium oxide catalysts. This catalyst was selected from our earlier work on methane to methanol conversion over mixed oxide systems. Calculations show that for defect free surfaces of the β-Ga 2O 3 phase only the (0 1 0) and (0 0 1) facets are stable. Density functional theory level calculations are presented which show that the (0 1 0) surface undergoes only a small amount of re-construction from the bulk structure. This suggests that the real crystal surfaces will be defective and we have attempted to increase the surface concentration of defects further by doping with divalent cations. Zn doping leads to an increase in activity compared to β-Ga 2O 3, whilst Mg doping decreased the activity.

Vibrational Optical Activity of (3S,6S)-3,6-Dimethyl-1,4-dioxane-2,5-dione

Vibrational circular dichroism (VCD), absorption, Raman, and Raman optical activity (ROA) spectra for the title compound, a cyclic dimer, were measured in non-aqueous solution. The vibrational normal modes are assigned based on the result from ab initio force field calculation. Harmonic frequencies and atomic polar tensors for simulation of IR absorption were calculated both on the (Hartree−Fock SCF) HF/6-31G** level and using density functional theory (DFT) methods with the Becke3/LYP hybrid functional. Magnetic transition dipole derivatives were calculated on the HF/6-31G level, and the ROA polarizability tensors were calculated on the HF/4-31G level. Excellent agreement between the DFT calculated and experimental frequencies was obtained without a need for scaling. Furthermore, using the DFT force field, the correct VCD sign and intensity patterns were reproduced as compared to the experimental mid-IR spectra. Reasonable near-IR VCD and mid-IR ROA sign patterns for the intense peaks were also calculated. The excellent agreement for the mid-IR VCD results shows that medium-sized, biologically relevant molecules can have their spectra simulated using quantum mechanical techniques to a high level, certainly one suitable for conformational analyses by direct comparison of theory to experimental results. Comparison of DFT and HF level calculations suggests that the improvement found using DFT methods is primarily due to the force field and not to the intensity parameters. DFT atomic polar tensors were systematically weaker than the HF generated ones. Weak coupling between the subunits of this dimer implies dominance by local interactions which suggests that useful extension of these calculational techniques to larger oligomers might be accomplished by transfer of parameters.

Dimerization of C60: The Formation of Dumbbell-Shaped C120

The structures of three possible C[sub 60] dimers with intact cages have been calculated at the semiempirical (MNDO/AM-1, PM-3) and ab initio density functional theory (DFT) levels. At the DFT level, both local (LDFT) and nonlocal (NLDFT) calculations have been performed. The dimers are formed by the 1,2-, 1,4-, and 1,2+1,4-cycloadditions of a cyclohexatrienyl unit of each C[sub 60]. The energies of the dimers relative to that of the most stable 1,2-C[sub 60] dimer are 74.0 kcal/mol (AM-1), 75.2 kcal/mol (PM-3), 69.7 kcal/mol (LDFT), and 76.2 kcal/mol (NLDFT) for the 1.4-C[sub 60] dimer and 93.0 kcal/mol (AM-1), 87.0 kcal/mol (PM-3), 69.8 kcal/mol (LDFT), and 69.5 kcal/mol (NLDFT) for the 1,2+1,4-C[sub 60] dimer. The dimerization reaction to form the C[sub 60] dimers from C[sub 60] is calculated to be weakly endothermic only for the formation of 1,2-(C[sub 60])[sub 2], and for the others, the reaction is predicted to be strongly endothermic. This result suggests that 1,2-cycloaddition is the most plausible scheme for the dimerization and polymerization of C[sub 60] molecules, if the cages remain intact. 47 refs., 4 figs., 8 tabs.