Theoretical investigation of vinylogous anomeric effect on 4-halo-4-H-pyran and 4-halo-4-H-thiopyran molecules

ABSTRACT

In this study, the stability of the 4-halo-4-H-pyran and 4-halo-4-H-thiopyran molecules in planar and puckered conformations was investigated in the B3LYP/6-311++G(d,p) level of theory. The total energy, dipole moment, the energies of frontier orbitals, and HOMO–LUMO gaps of the molecules were calculated. Natural bond orbital (NBO) analysis was used to illustrate vinylogous anomeric effect on the puckering of ring. The responsible interactions of this effect were determined. The interaction energy, off-diagonal elements and dipole moment values of their NBO were calculated. In addition, total steric exchange energy values of theses interaction were evaluated.     

Experimental and Theoretical Study of O-Substituent Effect on the Fluorescence of 8-Hydroxyquinoline

The synthesis and characterization of different ether and ester derivatives of 8-hydroxyquinoline have been made. UV-visible and fluorescence spectra of these compounds have revealed spectral dependence on both solvent and O-substituent. The fluorescence intensity of ether derivatives revealed higher intensity for 8-octyloxyquinoline compared with 8-methoxyquinoline, whereas those of ester derivatives had less fluorescence than 8-hydroxyquinoline. Theoretical calculations based on Time-dependent density functional theory (TD-DFT) were carried out for the quinolin-8-yl benzoate(8-OateQ) compound to understand the effect of O-substituent on the electronic absorption of 8-hydroxyquinaline (8-HQ). The calculations revealed comparable results with those obtained from the experimental data. Optimized geometrical structure was calculated with DFT at B3LYP/6-311++G** level of theory. The results indicated that 8-OateQ is not a coplanar structure. The absorption spectra of the compound were computed in gas-phase and solvent using B3LYP and CAM-B3LYP methods with 6-311++G ** basis set. The agreement between calculated and experimental wavelengths was very good at CAM-B3LYP/6-311++G** level of theory.     

Spectral (FT-IR,NMR) Analyses,Molecular Structures,and Chemical Bonding of Two Hexahydroacridine-1,8(2H,5H)-dione Derivatives: A Comparative Quantum Chemical Study

A comparative study on two hexahydroacridine-1,8(2H,5H)-dione deriv-atives namely, 9,10-bis(4-fluorophenyl)-3,3,6,6-tetramethyl-3,4,-6,7,9,10-hexahy-droacridine-1,8(2H,5H)-dione (FTHD) and 10-(4-fluorophenyl)-3,3,6,6-tetramethyl-9-(3,4,5-trimethoxyphenyl)-3,4,6,-7,9,10-hexahyd-roacridine-1,8(2H,5H)-dione (FTMPHD) has been performed. ¹H and ¹³C NMR spectra have been recorded in the CDCl₃ solvent. The equilibrium geometries of FTHD and FTMPHD have been determined and analyzed at DFT level employing B3PW91/6-311++G (d,p) method. The vibrational spectra of both the molecules are calculated and compared with the experimental FT-IR spectra. ¹H and ¹³C NMR spectra have been calculated by using the gauge-independent atomic orbital (GIAO) method. The calculated spectra have been found to be in good agreement with the experimental spectra. The quantum theory of atoms-in-molecule (QTAIM) approach is employed to study various intramolecular interactions within these molecules. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and the molecular electrostatic potential (MESP) surfaces have been constructed and analyzed. Various electronic as well as thermodynamic parameters have been reported.     

The influence of some new 2,5-disubstituted 1,3,4-thiadiazoles on the corrosion behaviour of mild steel in 1 M HCl solution: AC impedance study and theoretical approach

The new 2,5-disubstituted 1,3,4-thiadiazoles were investigated as corrosion inhibitors of mild steel in 1 M HCl using AC impedance technique. Four of these compounds exhibit good inhibition properties, while two of them, 2,5-bis(4-nitrophenyl)-1,3,4-thiadiazole and 2,5-bis(4-chlorophenyl)-1,3,4-thiadiazole, stimulate the corrosion process especially at low concentrations. The experimental data obtained from this method show a frequency distribution and therefore a modelling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. Possible correlations between experimental inhibition efficiencies and quantum chemical parameters such as dipole moment (μ), highest occupied (E_HOMO) and lowest unoccupied (E_LUMO) molecular orbitals were investigated. The models of the inhibitors were optimised with the Density Functional Theory formalism (DFT) using hybrid B3LYP/6-31G (2d,2p) as a higher level of theory. The Quantitative Structure Activity Relationship (QSAR) approach has been used and composite index of some quantum chemical parameters were constructed in order to characterize the inhibition performance of the tested molecules.     

Experimental and theoretical insight into the electronic properties of 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes

In this paper, spectroscopic and quantum mechanical investigation of nine 4-aryl-5-arylazo-3-cyano-6-hydroxy-2-pyridone dyes was performed, and obtained density functional theory (DFT) results were compared with experimental data. The structural and spectroscopic properties of azo-2-pyridone dyes were studied by DFT using B3LYP, CAM-B3LYP, and M06-2X methods with a 6-311++G(d,p) basis set. Comparison of results reveals that the scaled theoretical vibrational frequencies of azo dyes are in good agreement with experimental data. The time-dependent DFT calculated and experimental ultraviolet-visible (UV-vis) absorption spectra are also in good agreement. The effect of electron-donating –OCH₃ and electron-withdrawing –NO₂ groups on the structural parameters, vibrational frequencies, UV-vis absorption, and natural bond orbital (NBO) atomic charges were thoroughly analysed. Vibrational, UV-vis, and NBO analyses confirm that investigated dyes exist in the hydrazo tautomeric form in the solid state and ethanol solution. These analyses signify the occurrence of intramolecular charge transfer in these azo-pyridone dyes.     

Synthesis,Structural, and Theoretical Studies of Quinazoline-2,4-dione Derivatives

New quinazolin-2,4-dione derivatives have been synthesized and fully characterized. The new derivatives were synthesized using 3-(2-imino-4-oxo-3H,4H,5H-thiazolidin-3-yl)-1H-quinazolin-2,4-dione by nucleophilic addition mechanism. DFT calculations using B3LYP/6–311++G(d,p) level of the theory were used to investigate the molecular structures and the relative stabilities of the anticipated isomers (E and Z). Both experimental and theoretical calculations confirmed the higher stability of the Z-isomers compared to the E-isomers. The former is stabilized by two intramolecular hydrogen bonds compared to only one in the latter isomer. The frontier orbital calculations (HOMO and LUMO), and the energy gap confirmed the stability of the molecules.     

Does Prop-2-ynylideneamine,HC≡CCH=NH,Exist in Space? A Theoretical and Computational Investigation

MP2, DFT and CCSD methods with 6-311++G** and aug-cc-pvdz basis sets have been used to probe the structural changes and relative energies of E-prop-2-ynylideneamine (I), Z-prop-2-ynylideneamine (II), prop-1,2-diene-1-imine (III) and vinyl cyanide (IV). The energy near-equivalence and provenance of preference of isomers and tautomers were investigated by NBO calculations using HF and B3LYP methods with 6-311++G** and aug-cc-pvdz basis sets. All substrates have Cs symmetry. The optimized geometries were found to be mainly theoretical method dependent. All elected levels of theory have computed I/II total energy of isomerization (ΔE) of 1.707 to 3.707 kJ/mol in favour of II at 298.15 K. MP2 and CCSD methods have indicated clearly the preference of II over III; while the B3LYP functional predicted nearly similar total energies. All tested levels of theory yielded a global II/IV tautomerization total energy (ΔE) of 137.3–148.4 kJ/mol in support of IV at 298.15 K. The negative values of ΔS indicated that IV is favoured at low temperature. At high temperature, a reverse tautomerization becomes spontaneous and II is preferred. The existence of II in space was debated through the interpretation and analysis of the thermodynamic and kinetic studies of this tautomerization reaction and the presence of similar compounds in the Interstellar Medium (ISM).     

Synthesis of new silica xerogels based on bi-functional 1,3,4-thiadiazole and 1,2,4-triazole adducts

New transparent Silica-based hybrid materials were synthesized by reaction of polymethylhydrosiloxane (PMHS) and organic compounds: 1,3,4-thiadiazole-2,5-diamine (1), 1,3,4-thiadiazole-2,5-dithiol (2) and 1H-1,2,4-triazole-3-thiol (3), in tetrahydrofuran as solvant using hexachloroplatinic acid (H₂PtCl₆.6H₂O) as a catalyst. PMHS was used as a principal network forming agent, it has been cross-linked via hydrosilylation reaction with bi-functional heterocyclic compounds, leading to the formation of colored gels. These later dried (xerogels) were characterized by numerous techniques, including spectroscopy of (FT–IR) and ¹³C and ²⁹Si CP MAS NMR. The xerogels morphology and texture were studied by scanning electron microscopy and Brunauer–Emmet–Teller method. According to N₂-physisorption results, isotherms are classified as type IV with H₂ type hysteresis loop; then, the xerogels are mesoporous materials. The optic and magnetic properties of the obtained materials were studied by UV–VIS and EPR spectroscopies, respectively. This study showed that all materials are paramagnetic semiconductors.     

Fatty Acids in Heterocyclic Synthesis Part XII: Synthesis of Surfactants from Pyrazole, Isoxazole, Pyrimidine and Triazine, Incorporating the 1,3,4-Thiadiazole Moiety Having Dyeing and Antimicrobial Activities

The titled compounds were prepared from 2-amino-5-heptadecyl[1,3,4]thiadiazole (1). Diazotization of (1) produced (2) which was coupled with active methylene compounds and gave azo ⇌ hydrazono derivatives (3A, 3B) _a–d . It was found that there is regio-specificity for addition of different nucleophiles to these tautomers; thus, nitrogen nucleophiles such as hydrazine hydrate, hydroxylamine hydrochloride and thiourea were reacted via Azo tautomer (3A) to yield pyrazole, isoxazole and pyrimidine respectively (5-7), while carbon nucleophiles as phenylisocyanate was reacted via the hydrazono tautomer (3B) and produced triazine derivatives (4). Additionally, the diazonium chloride (2) was coupled with alkaline 2-naphthol and produced 2-(5-heptadecyl-[1,3,4]thiadiazol-2-yl)-1,2-dihydro-3-oxa-1,2-diaza-cyclopenta[a]naphthalene (8). UV–visible spectra of the synthesized colored compounds (2-8) showed λ _max at 374–398 nm, while screening these compounds in vitro against micro-organisms (including structure-activity relationship SAR study) revealed high antibacterial and moderate antifungal activities. Propoxylation of compounds 1, 3, 5, 6, 7 and 8 with 3, 5, 7 mol of propylene oxide produced nonionic surfactants I(a–c)–IX(a–c) having surface active properties so, it is clear that the tested surfactants can be used in the manufacture of dyes, drugs, cosmetics, emulsifiers, pesticides, luminphores for optical applications and many other industries with low toxicity to human beings and the environment owing to their high solubility and good biodegradability.     

Novel ceramides and a new glucoceramide from the roots of <Emphasis Type="Italic">Incarvillea arguta</Emphasis>

Novel ceramides, rel-(3S,4S,5S)-3-[(2R)-2-hydroxycosanoyl-hexacosanoylamino]-4-hydroxy-5-[(4Z)-tetradecane-4-ene]-2,3,4,5-tetrahydrofuran (1a-g), and a new glucoceramide, 1-O-β-d-glucopyranosyl-(2S,3S,4R,8E)-2-[(2R)-2-hydroxytetracosanoylamino]-1,3,4-octodecanetriol-8-ene (2) were isolated from the aqueous ethanolic extract of the roots of Incarvillea arguta, together with eight known compounds: β-sitosterol (3), oleanolic acid (4), ursolic acid (5), piperin (6), maslinic acid (7), β-sitosterol 6′-O-acyl-β-d-glucopyranoside (8), 8-epideoxyloganic acid (9), and plantarenaloside (10). Their structures were elucidated on the basis of spectral data including IR, MS, NMR [¹H NMR, ¹³C NMR (distortionless enhancement by polarization transfer), ¹H−¹H COSY, heteronuclear multiplequantum coherence, and heteronuclear multiple-bond coherence correlations]. The relative configurations were established by nuclear Overhauser effect spectroscopy experiments and by comparison of the NMR spectral data and coupling constants with those already reported in the literature.     

Electronic structures and photophysical properties of carbazole- and thiophene-based organic compounds used as hole-injecting layer for organic light-emitting diodes (OLEDs)

In this study, we have carried out a theoretical study on six organic compounds based on thiophene and carbazole, with the aim of using them as a hole-injecting layer of organic light-emitting diodes (OLEDs). In this study, we have tested two types of structures: D-π-D for MO1, MO2, MO3, and MO4 compounds and D-π-A for MO5 and MO6 compounds. The correlation structure-properties of these studied compounds have been proceeded and discussed by analyzing highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy gap, polarization effect, atom transition density matrix, absorption, and photoluminescence (PL). This theoretical study, based on density functional theory (DFT)/TPSSTPSS/aug-cc-pVQZ and the integral-equation-formalism polarizable continuum model/Coulomb attenuated method-Becke, 3-parameter, Lee–Yang–Parr (IEFPCM/TD-CAM-B3LYP)/6-31++G(d,p) is consolidated by experimental data for MO1, MO2, and MO4 compounds, allowing the determination of their structural and optoelectronic properties (HOMO, LUMO, gap [Eg], absorption, and emission parameters). The obtained results appear very conclusive and show that the performance of these compounds in terms of luminescence, absorption, and current–voltage (I–V) characteristics of OLED devices make them a promising candidate for the realization of light-emitting diodes.     

DFT study of the molecular structures,infrared and Raman spectra of 1,5-dichloropenta-1,4-diyn-3-one, 1,5-dibromopenta- 1,4-diyn-3-one, 1,5-diiodopenta-1,4-diyn-3-one,their sulfur,and selenium analogues

1,5-Dichloropenta-1,4-diyn-3-one, 1,5-dibromopenta-1,4-diyn-3-one, 1,5-diiodopenta-1,4-diyn-3-one, their sulfur, and selenium analogues have been studied, in the gas phase, in C _2v symmetry, using density functional theory method. The functional used is B3LYP and the basis sets employed are 6-311++G(d,p) for all atoms except that 6-311G(d,p) has been used for iodine atom only. Molecular parameters, namely bond lengths, bond angles, rotational constants, dipole moments, and energies are predicted for these 1,5-dihalogenoketones. Atomization energies and natural charges on the atoms have also been predicted. Further, vibrational infrared spectra parameters, namely harmonic vibrational frequencies and absolute intensities, Raman activities, and depolarization ratios are also reported. It is generally found that halogens substitution lead to only small steric and geometric perturbations in the 1,5-dihalogenoketones. However, the literature for these 1,5-dihalogenoketones is very limited and therefore data from the present study could be used for their characterization as and when they are synthesized.     

New ceramides from <Emphasis Type="Italic">Rantherium suaveolens</Emphasis>

A mixture of five new ceramides was isolated from the aerial parts of Rantherium suaveolens and characterized by spectroscopic and chemical methods. Their structures were elucidated by spectroscopic and chemical methods as (2S, 3S, 4R, 2′R, 14E)-2-(2′-hydroxydocosanoylamino)-14-octadecene-1,3,4-triol (1), (2S,3S,4R,2′R, 14F)-2-(2′-hydroxytricosanoylamino)-14-octadecene-1,3,4-triol (2), (2S,3S,4R,2′R,14F)-2-(2′-hydroxytetracosanoylamino)-14-octadecene-1,3,4-triol (3), (2S,3S,4R,2′R,14E)-2-(2′-hydroxypentacosanoylamino)-14-octadecene-1,3,4-triol (4), and (2S,3S,4R,2′R,14E)-2-(2′-hydroxyhexacosanoylamino)-14-octadecene-1,3,4-triol (5).     

Structural and Optical Properties of New Naphthalene and Perylene Imide Imidazoles

ABSTRACT

New unsymmetrically substituted naphthalene and perylene imide imidazoles, N-(2-ethylhexyl)-naphthalene-3,4-(4,5-dicyano-1,2-benzimidazole)-9,10-dicarboxyimide and N-(1-heptyloctyl)-perilene-3,4-(4,5-dicyano-1,2-benzimid-azole)-9,10-dicarboxyimide, were synthesized via condensation reactions of diaminophthalonitrile and aromatic monoimide monoanhydride derivatives. Their structural analyses have been conducted by using general spectroscopic methods including FT-IR, ¹H- and ¹³C-NMR, mass and elemental analysis. The molecular structure of naphthalene derivative was also determined by single crystal x-ray diffraction. Electronic absorption and emission properties were investigated on comparison. For studied compounds, both DFT and TDDFT calculations were carried out with the 6-311G(d,p) basis set, taking into account solvation effects by means of polarizable continuum model as implemented in the Gaussian 09 package.     

Quantum chemical studies on molecular conformations,energetic and intramolecular hydrogen bonding in ground and electronic excited state of (thioxosilyl) ethyleneselenol

In this work, a conformational analysis of (thioxosilyl) ethyleneselenol was performed using several computational methods, including density-functional theory (DFT) (B3LYP), MP2 and G2MP2. Harmonic vibrational frequencies were estimated at the same levels to confirm the nature of the stationary points found and also to account for the zero point vibrational energy correction. MES-1 and TES-1 conformers exhibit hydrogen bonding. This feature, although is not the dominant factor in the stability of conformers, appears to be of foremost importance to define the geometry of the molecule. Two intramolecular hydrogen bonds established between the polar groups were identified by the structural geometric parameters. These involved the thiol and selenol functional groups and were identified and characterized by the frequency shift in their stretching vibration modes. Furthermore, the excited-state properties of intramolecular hydrogen bonding have been investigated theoretically using the time-dependent DFT method. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen bonding was considered using the PCM (polarizable continuum model), SCI-PCM (self consistent isodensity-polarizable continuum model) and IEF-PCM (integral equation formalism-polarizable continuum model) methods. The “atoms in molecules” theory of Bader was used to analyze critical points and to study the nature of hydrogen bond in these systems. Natural bond orbital (NBO) analysis was also performed for better understanding the nature of intramolecular interactions. The calculated highest occupiedmolecular orbital and lowest unoccupied molecular orbital energies show that charge transfer occur within the molecule. Further verification of the obtained transition state structures was implemented via intrinsic reaction coordinate analysis. Calculations of the ¹H NMR chemical shift at the GIAO/B3LYP/6–311++G** level of theory are also presented.     

Mechanistic investigation of the reaction of thiourea with dialkyl acetylenedicarboxylates: a theoretical study

In this work, mechanistic investigation of the addition–cyclization reaction between thiourea (TU) and dialkyl acetylenedicarboxylate (DAAD) was made theoretically with the B3LYP method using a 6-311++G(2d,2p) basis set. In order to investigate the effect of substituted alkyl groups, the reaction was evaluated in the presence of dimethyl acetylenedicarboxylate, diethyl acetylenedicarboxylate and di-tert-butyl acetylenedicarboxylate. To evaluate the effect of structure and dielectric constant of the solvent, all structures were optimized in different solvent phases such as dichloromethane and acetone at the B3LYP/6-311++G(2d,2p) level of theory. Different orientations of alkyl groups make different kinetic paths. Results indicated that the reaction mechanism did not change with different orientations of COOMe, COOEt or COOtBu groups, but caused significant changes in the potential energy surfaces of the reaction coordinate. The reaction product (alkyl E-2-(2-imino-4-oxo-1,3-thiazolane-5-yliden) acetates) can be converted to different tautomeric forms in two proton transfer processes. So, in order to investigate the effect of different substituted alkyl groups, intermolecular proton transfer in the product was investigated both in gas phase and in the presence of methanol, ethanol and tert-butanol molecules as a bridge to facilitate the proton transfer process.     

Synthesis,characterization, and dielectric properties of polymers functionalized with coumarone and diethanolamine

A series polymers of the poly(4‐{[bis(2‐hydroxyethyl)amino]methyl}‐2‐oxo‐2H‐chromen‐7‐yl‐2‐methylpropanoate), P(CIMMAOC)‐DEA, were synthesized by modification of poly(4‐(chloromethyl)‐2‐oxo‐2H‐chromen‐7‐yl‐2‐ethylpropanoate), P(CIMMAOC), with diethanolamine (DEA). All polymers were structurally characterized by FTIR, ¹H NMR, UV–vis, and Fluorescence spectra. The electronic features of the polymer, such as lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energies and electrostatic potential (ESP), and the vibrational frequencies were computed by the Becke3–Lee–Yang–Parr (B3LYP) functional using 3–21G* basis set. Dielectric measurements for P(CIMMAOC) and P(CIMMAOC)‐DEA were performed by means of an impedance analyzer as a function of frequency and temperature. It was found that the dielectric constant values decreased in the applied frequency range. The values of dielectric constant increased with a rise in concentrations of DEA in polymer for all temperatures. Dielectric constants of P(CIMMAOC) and P(CIMMAOC)‐DEA (60%) were calculated as 3.93 and 12.29 at 1 kHz, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42164.     

A facile synthesis of some novel fused [1,2,4]triazolo[3,4-b][1,3,4]thiadiazol derivatives

A series of novel 3-[6-(4-substituted phenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazol-3-ylmethyl]-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one derivatives (7a–7h) have been synthesized from 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carbonitrile (1) through a multi-step reaction sequence. The key intermediate (6) on condensation with various substituted aromatic carboxylic acids in the presence of phosphorus oxychloride afforded the series of title compounds (7a–7h). The structures of all newly synthesized compounds were established on the basis of their IR, ¹H-NMR, ¹³C-NMR and liquid chromatography mass spectrometry spectral data.