Víctor M. Chapela

Meritorious Autonomous University of Puebla, Ejido Puebla, Baja California, Mexico

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Publications (69)104.1 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: We report single crystal X-ray diffraction (hereafter, SCXRD) analyses of derivatives featuring the electron-donor N-ethylcarbazole or the (4-diphenylamino)phenyl moieties associated with a -CN group attached to a double bond. The compounds are (2Z)-3-(4-(diphenylamino)-phenyl)-2-(pyridin-3-yl)prop-2-enenitrile (I), (2Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-4-yl)-prop-2-enenitrile (II) and (2Z)-3-(9-ethyl-9H-carbazol-3-yl)-2-(pyridin-2-yl)enenitrile (III). SCXRD analyses reveal that I and III crystallize in the monoclinic space groups P2/c with Z' = 2 and C2/c with Z' = 1, respectively. Compound II crystallized in the orthorhombic space group Pbcn with Z' = 1. The molecular packing analysis was conducted to examine the pyridine core effect, depending on the ortho, meta- and para-positions of the nitrogen atom, with respect to the optical properties and number of independent molecules (Z'). It is found that the double bond bearing a diphenylamino moiety introduced properties to exhibit a strong π-π-interaction in the solid state. The compounds were examined to evaluate the effects of solvent polarity, the role of the molecular structure, and the molecular interactions on their self-assembly behaviors. Compound I crystallized with a cell with two conformers, anti and syn, due to interaction with solvent. DFT calculations indicated the anti and syn structures of I are energetically stable (less than 1 eV). Also electrochemical and photophysical properties of the compounds were investigated, as well as the determination of optimization calculations in gas and different solvent (chloroform, cyclohexane, methanol, ethanol, tetrahydrofuran, dichloromethane and dimethyl sulfoxide) in the Gaussian09 program. The effect of solvent by PCM method was also investigated. The frontier HOMO and LUMO energies and gap energies are reported.
    Full-text · Article · Mar 2016 · Molecules
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    [Show abstract] [Hide abstract] ABSTRACT: The reaction of the nitroxy radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) with Br2 has been investigated with CCl4 and hexane to obtain TEMPO-Br salts: 2,2,6,6-tetramethylpiperidine-1-oxopiperidine tribromide [TEMPO][Br3] (I), and the 1-hydroxy-2,2,6,6-tetramethylpiperidinium bromide salts [TEMPH+OHBr-] (II and III). The salt I was isolated in crystalline form directly from the synthesis and II and III by only changing the solvent. The crystals of I belong to the orthorhombic crystal systems with space group Cmc21, a = 10.5596(4) Å, b = 14.0464(4) Å, c = 9.4202(5), and with asymmetric unit of Z = 4. Crystals II belong to Pnna a = 11.9860(3) Å, b = 23.6720(9) Å, c = 7.7051(3) Å while III belongs to Cmc21 with a = 10.2686(3) Å, b = 10.7661(3) Å, c = 10.0274(2) Å; the asymmetric unit of II and III was Z = 8 and Z = 4, respectively. The crystal structure of I shows the Br3 ion as [Br-Br-Br]- for each molecule of TEMPO. The crystal structure of II shows a weak intermolecular hydrogen bond between -N-H⋯Br(1) and O(1)H⋯Br(2) due to the presence of the -N+HOH- moiety. In contrast, crystal III shows intermolecular hydrogen bonding between O(1)H⋯Br(1)⋯HN(1) due to the -N+HOH- moiety. The resulting compounds were characterized by FT-IR and UV-vis spectroscopy. The structural parameters have been compared with the related hydroxylaminotrichlorosilane known from the literature and with results of DFT calculations.
    Full-text · Article · Oct 2015
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    [Show abstract] [Hide abstract] ABSTRACT: We report the results from the reactions of 1-phenylethanol, 2-methylpropanol, trimethylsilanol and triphenylsilanol with TEMPO, OH-TEMPO and Br-TEMPO salt at different reaction conditions to obtain model functionalized compounds. With 1-phenylethanol, the ketone compound was obtained as expected, but when using triphenylsilanol the corresponding hexaphenyldisiloxane [di(triphenylsilane)ether] was obtained in crystal form, as well as the silaneoxiamine (Si-O-N). The hexaphenyldisiloxane crystal belonged to the triclinic crystal system with a space group P[1 with combining macron], a = 8.5829(4) A, b = 9.4856(4) A, c = 10.9694(5) A, [small alpha] = 95.951(4)[degree], [small beta] = 90.059(3)[degree], [gamma] = 113.352(4)[degree], the asymmetric unit comprised of Z = 1. The results showed that the synthetic method to obtain silane ether is simple and can be completed in one step, as well as independently of the type of TEMPO and base used. Also, under the same reactions conditions, we prepared the corres
    Full-text · Article · Sep 2015 · RSC Advances
  • [Show abstract] [Hide abstract] ABSTRACT: The synthesis and characterization of the precursor isomers trans-4-(2-(pyridin-2-yl)vinylbenzaldehyde (I), trans-4-(2-(pyridin-4-yl)vinylbenzaldehyde (II), trans-4-(2-(pyridin-2-yl)vinylbenzoic acid (III) and (E)-4-(2-(pydridin-4-yl)vinylbenzoic acid (IV) are reported. These compounds were prepared in order to obtain trans-4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO (V). Compounds I and II were obtained by using a Knoevenagel reaction in the absence of a condensing agent and solvent. Oxidation of the aldehyde group using the Jones reagent afforded the corresponding acid forms III and IV. A condensation reaction with 4-amino-TEMPO using oxalyl chloride/DMF/CH2Cl2 provided the 4-((E)-2-(pyridin-2-yl)vinyl)benzamide-TEMPO. Single crystals of compounds I, II and III were obtained and characterized by X-ray diffraction. Compound I belongs to space group P21/c, a = 12.6674(19) Å, b = 7.2173(11) Å, c = 11.5877(14) Å, β = 97.203(13)° and the asymmetric unit was Z = 4, whereas compound II was in the space group P21, with a = 3.85728(9) Å, b = 10.62375(19) Å, c = 12.8625(2) Å, β = 91.722 (2)° and the asymmetric unit was Z = 2. Compound III crystallized as single colorless needle crystals, belonging to the monoclinic system with space group P21, with Z = 2, with a = 3.89359(7) Å, b = 17.7014(3) Å, c = 8.04530(12) Å, β = 94.4030 (16)°. All compounds were completely characterized by IR, 1H-NMR, EI-MS and UV-Vis.
    No preview · Article · Apr 2015 · Molecules
  • [Show abstract] [Hide abstract] ABSTRACT: The structure of the Schiff base (E)-2-[(2-hydroxybenzylidene)amino]phenylarsonic[(E)-HBAPhAA], synthesized from salicylaldehyde and o-aminophenylarsonic acid in the presence of HCl, was characterized by FTIR, H-1 NMR, EI-MS, UV-Vis spectroscopy, and X-ray crystallography. The crystal belonged to the monoclinic space group P2(1)/c. Two molecules formed a dimer via intermolecular interactions due to the attachment of H atoms to 01, 03 and 04 with 0 H bond distances within reasonable ranges, ca. 0.84(3) angstrom. The structure also showed two intramolecular interactions of 2.634(2) and 3.053(2) angstrom for N-H center dot center dot center dot O hydrogen bonds, which caused the structures to be almost planar. We performed a theoretical analysis using OFT theory at B3LYP/6-31+G(d,p) level to determine the stability of the E and Z conformers. The geometry analysis of the E- and Z-isomers revealed an interconversion energy barrier between E/Z isomers of 22.72 kcal mol(-1). We also theoretically analyzed the keto form of the E-isomer and observed a small energy barrier for the tautomerization of 6.17 kcal moll.
    No preview · Article · Feb 2015 · Journal of Molecular Structure
  • [Show abstract] [Hide abstract] ABSTRACT: The ability of a series of isomers of the Schiff base (E)-2-(2-hydroxybenzylideneamino) phenylarsonic acid to inhibit corrosion is evaluated on the basis of their electronic properties, using their energy levels of the frontier molecular orbitals, dipole moments, and atomic and group charges. The different isomers are obtained by attaching the hydroxy substituent at different positions of the phenyl ring. The molecular electronic properties for each isomer are theoretically calculated by DFT methods in M06L/cc-pVTZ level and using as the basis set for the As atom the effective core potential of Hay and Wadt, LanL2DZ. The relationship between the inhibition efficiency and the molecular structure and electronic properties is evaluated using linear regression analysis. This study provides insights into the effect of the position of the -OH substituents and -AsO3H2 on the structure of the Schiff base.
    No preview · Article · Dec 2014 · International journal of electrochemical science
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    [Show abstract] [Hide abstract] ABSTRACT: The molecular structure and molecular interactions of an [small alpha],[small beta]-unsaturated nitrile, such as the interaction between adjacent molecules of (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridin-2-yl)-acrylonitrile (Z-DPPyACN) throughout the 4-diphenylamino moiety with the phenyl and pyridyl rings, play an important role in the self-assembly behaviors and optical properties of its powder and single-crystal forms. The crystal packing exhibits multiple C-H[small pi] and CHHC edge-to-face interactions that contribute to the supramolecular network between adjacent molecules. The resulting molecular structure resembles a pinwheel which exhibits a strong emission intensity at three different wavelengths. The crystal belongs to the monoclinic space group P21/n, with dimensions a = 12.9551(2), b = 11.29300(15), c = 14.6992(3) A, [small beta] = 115.648(2)[degree] and Z = 4. The single-crystal compound shows three emission maxima at 533, 569, and 607 nm, whereas the powder and the molecules in an aggregated state show maximum emission intensities that are dependent on the nature of the solvent. The Z-DPPyACN dye's optical properties show a Stokes shift caused by the reorganization of the molecule in the excited state, as effected by the solvent polarity. This indicates a large change in the dipole moment of dye molecules upon excitation due to an intramolecular charge transfer interaction. From a theoretical point of view, the molecular geometry, electronic structure, and excitation energies are reported using density functional theory and compared with the experimentally determined one photon absorption and emission spectra.
    Full-text · Article · Sep 2014 · CrystEngComm
  • [Show abstract] [Hide abstract] ABSTRACT: The effect of the ratio of oxygen to carbon atoms (O/C) on the morphology of carbon nanostructures has been studied by varying the methanol and ethanol ratio in the reaction mixtures. Notable morphological differences in the synthesized carbon nanostructures are observed as a function of the O/C ratio. At a high O/C ratio, i.e., using methanol (O/C = 1), the synthesized carbon nanoshells (CNS) are faceted. Moreover, other faceted nanostructures, such as triangular and hexagonal, are observed in this strong oxidative environment. Decreasing the O/C ratio in the mixture by adding ethanol induces changes in the CNSs morphology; they are less faceted and favor only the growth of single-walled carbon nanotubes mixed with the CNSs. The importance of the O/C ratio is corroborated by replacing ethanol (O/C = 0.5) with polyethylene glycol (O/C = 0.5) in the methanol:ethanol reaction mixture. Finally, at very low O/C ratios, i.e., methanol:octanol mixtures, CNS are obtained and no faceted nanostructures or SWCNT are found. Thus, adjusting the O/C ratio is a method for obtaining high purity samples of CNS. Moreover, the use of the alcohols during the synthetic process is a simple and green method of functionalizing CNS.
    No preview · Article · Sep 2014 · Carbon
  • [Show abstract] [Hide abstract] ABSTRACT: The properties of aqueous solutions of polyelectrolytes of sodium o- and p-methacryloylaminophenylarsonate (o- and p- MAPHA-Na) with acrylamide (AAD) or sodium methacrylate (MA-Na): poly(sodium o-methacryloylaminophenylarsonate) (poly(o-MAPHA-Na)), poly(sodium o-methacryloylaminophenylarsonate-co-acrylamide) (poly(o-MAPHA-Na-co-AAD)) (26:74), poly(sodium o-methacryloylaminophenylarsonate-co-sodium methacrylate) (poly(o- MAPHA-Na-co-AM-Na) (35:65) and (14:86), and poly(sodium p-methacryloylaminophenylarsonate-co-sodium methacrylate) (poly(p- MAPHA-Na-co-AM-Na)) (34:66) were studied by off-line, multi-angle light scattering, and in-line using size exclusion chromatography coupled with multi-angle light scattering (SEC-MALS) and refractometric (RI) detection. The Mw value corresponding to the homopolymer poly(o-MAPHA-Na) was 1,300,000 g/mol and for the copolymers the Mw and gyration radius values were decreased when the AAD or AM-Na comonomer composition increased. The macromolecular parameters obtained using SEC-MALS were in agreement with the values measured in the off-line mode. Also, SEC-MALS experiments allowed examination of the radius of gyration-Mw relationship in order to determine the polyelectrolyte conformation (ρ) in solution; these values fell between 0.7-0.53, indicating that the polyelectrolytes are random coils at θ-conditions. In addition, the effect of the pH on the macromolecular parameters was evaluated. At pH 4.5, the Mw and gyration radius values corresponding to poly(o-MAPHA-Na) and poly(o-MAPHA-Na-co-AAD) (26/74) remained very close to those measured at pH 7. However, <r g 2 > values for poly(o-MAPHA-Na-co-AM-Na) copolymers at pH 4.5 were less than pH 7, indicating that the presence of AM-Na reduced the size of the copolymer through intermolecular interactions.
    No preview · Article · Aug 2014 · Journal of Polymer Research
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    [Show abstract] [Hide abstract] ABSTRACT: The novel compound Z-2-phenyl-3-(4-(pyridin-2-yl)phenyl)acrylonitrile (PPyPAN) was synthesized from the condensation reaction between phenylacetonitrile and 4-(pyridin-2-yl)benzaldehyde. This compound crystallizes in two forms: polymorph I (triclinic, P - 1, Z' = 2) and polymorph II (orthorhombic, Pbc2(1), Z' = 2). The molecular structures and optical properties of the two polymorphs have been characterized via H-1 NMR, El, FTIR, UV-Vis spectroscopy, DSC, single-crystal and XRPD. The molecular structure, packing properties, and intermolecular interactions were examined for both polymorphs of PPyPAN in order to interpret the emission properties. A subtle change in the molecular conformation (e.g., a rotation around single C-C bonds) found for both polymorph plays an important role in their solid-state properties. The structure and optical properties of the new structures were well characterized and showed unique features for both polymorphic phases. For phase I, we observed an excitation spectrum with an lambda(ex) at 325-346 nm, which is the maximum excitation or absorption wavelength for the lowest S-0 -> S-1 transition, which is characteristic to the pi-pi* transition, and an emission spectrum with an lambda(max)(em) at 454 nm. For phase II, the excitation spectrum showed an lambda(max)(ex) at 325 nm, whereas the lambda(max)(em) showed a red-shift to 492 nm.
    Full-text · Article · May 2014
  • [Show abstract] [Hide abstract] ABSTRACT: Two novel ATRP initiator (R-X): 2-bromo-2-methyl-N-(1-phenyl-ethyl)propanamide (I) and 2,2,2-trichloro-N-(1-phenylethyl)acetamide (II) were synthesized and characterized by 1H-NMR, IR, EI. Also, crystal structures of (I) and (II) are reported. Compounds (I) and (II) were used in the ATRP reaction of methyl methacrylate (MMA) and acrylamide (AAD) at 48°C, using CuBr/Me6TREN and ethanol/toluene (60:40) mixture as catalytic complex and solvent, respectively. End-group analysis by 1H-NMR was used to determinate the molecular mass of the polymers synthesized via ATRP. The Mn values for poly(MMA) using (II) were 2333 and 3952 g/mol, which is higher in comparison with the Mn values obatined for (AAD)/(II) and (AAD)/(I) systems indicating that monomers containing ester moiety in their structure, such as acrylates and methacrylates, may be good candidates to polymerize with (II) and CuBr/Me6TREN.
    No preview · Article · May 2014 · Macromolecular Symposia
  • V Chapela · M Percino · F Calvo · L Trinidad
    No preview · Chapter · Apr 2014
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    [Show abstract] [Hide abstract] ABSTRACT: In this review paper, have been investigated three novel crystal structures of three molecules with carbazole substituents as the electron-donor group. These molecules, 2-(phenyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile (I), 2-(3''- pyridyl)-3-(N-ethyl-(3'-carbazolyl))acrylonitrile (II), and 2-(4-pyridyl)-3-(N-ethyl-(3´-carbazolyl))acrylonitrile (III) in their structure, possess the electron-donor carbazole moiety, a -CN group attached to the double bond, and a phenyl or a pyridine function at the meta- or para-position. It was revealed with the help of single crystal diffraction X-ray analysis that there exists no difference in the crystal system, because all the compounds were crystallized in monoclinic system with space group P21/c. For determining the effect of the position of the nitrogen atom substitution on the crystal properties, has been analyzed and contrasted the molecular packing in a single crystal with that of other previously reported carbazole derivatives. The double bond bearing N-ethylcarbazole,–CN, phenyl or pyridine groups was observed to impart sufficient polarity in order to show slipped π-stacking aggregation in the solid state, affecting the compounds in the solid state and consequently affecting their fluorescence properties. The substitution at the para position was reported to exhibit more multiple C-H...π interactions as well as an interesting and unexpected short contact distance between adjacent N...N molecules those brought a conformational change resulting in an edge-to-face alignment in the molecules and affecting the best relative photoluminescence efficiency of the sample.
    Full-text · Article · Mar 2014
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    [Show abstract] [Hide abstract] ABSTRACT: The structural characterisation of the molecule 1,4-bis[2-cyano-2-(o-pyridyl)ethenyl] benzene obtained through Knoevenagel condensation is reported. The single crystals, as light brown rods, were cultured from a chloroform solution using a slow evaporation method at ambient temperature. The compound crystallised in the monoclinic system belonging to the C2/c space group with a = 26.4556(9) Å, b = 3.73562(10) Å, c = 18.4230(6) Å, β = 109.841(4)° and the asymmetric unit comprising Z = 4. The structure is ordered and the molecules of the title compound exhibited a lattice with water molecules located at sites of inversion and two-fold axial symmetries. Thus, only halves of the molecules are symmetrically independent. The lattice is reported and contrasted with X-ray single-crystal diffraction and theoretical calculations of 1,4-bis(1-cyano-2-phenylethenyl)benzene. By using density functional theory (DFT) and second order Moller-Plesset (MP2) theoretical calculations, the ground state geometry in the whole molecule at the B3LYP/6-31+G(d,p), and MP2/6-31+G(d,p) theory levels, respectively, were optimised. The DFT calculations showed a quasi-planar structure of the molecule, whereas the wave function-based MP2 method afforded a non-planar optimised structure with significant torsion angles between the pyridine and phenyl rings.
    Full-text · Article · Feb 2014 · Chemical Papers- Slovak Academy of Sciences
  • [Show abstract] [Hide abstract] ABSTRACT: The 1-phenyl-2-(α-pyridyl)ethanol [or 1-phenyl-2-(2-pyridyl)ethanol] compound was obtained from the Knoevenagel condensation reaction between 2-methylpyridine with benzaldehyde without catalyst or solvent. The compound was characterized by IR, 1H-NMR, and by single crystal X-ray diffraction. The X-ray structure clearly revealed that the compound crystallizes in a monoclinic system with centrosymmetric space group, P21/c, with Z′ = 1. The unit cell dimensions are a = 5.2481(3), b = 8.2862(4), c = 23.8498(14) Å, and β = 96.761(5)°. The crystal structure showed the formation of one intermolecular hydrogen bond O–H···N between the oxygen atom of the O–H and the nitrogen atom of the pyridine group of the adjacent molecule. The crystallography data gave evidence that the intermediate compound is a new stable 1-phenyl-2-(2-pyridyl)ethanol intermediate which presents an interesting relationship between stability and hydrogen bonds formation in the structure for obtaining similar compounds that have been proposed in the literature. Also, it is shown that it is just before the dehydration process which yields the trans double bond of the 1-phenyl-2-(2-pyridyl)ethene.
    No preview · Article · Jun 2013 · Research on Chemical Intermediates
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    [Show abstract] [Hide abstract] ABSTRACT: Knoevenagel condensation of phenylacetonitrile with 4-diphenylaminophenylacetonitrile in the presence of piperidine was carried out to obtain a novel conjugated compound. In addition to the expected compound 2-(phenyl)-3-(4-diphenylaminophenyl)acrylonitrile (I), the 3-((4-diphenylamino)phenyl)-2,4-diphenylpentanedinitrile (II) was also obtained with a good yield. Compound II was obtained as a result of the Michael addition of phenylacetonitrile with 2-(phenyl)-3-(4-diphenylaminophenyl)acrylonitrile (I). Conversely, when the same reaction was performed in the presence of KOH as catalyst, only the α,β-unsaturated nitrile (I) was afforded with a 92 % yield. The structures were confirmed with IR, EI-MS and NMR spectroscopy. Single crystals I and II were formed and their structures were determined by X-ray single-crystal diffraction analysis. Crystal I belongs to the monoclinic system with space group P21/n having unit cell parameters of a = 16.8589(5) Å, b = 6.68223(17) Å, c = 19.8289(7) Å, β = 111.133(4)○ and Z = 4. Crystal II belongs to the same monoclinic system with space group P21/c, having unit cell parameters of a = 10.8597(4) Å, b = 24.7533(10) Å, c = 9.7832(4) Å, β = 91.297(3)○ and Z = 4. In addition to the structural data analysis, some theoretical calculations that reveal the nature of relevant structure-property relationships are also reported.
    Full-text · Article · May 2013 · Chemical Papers- Slovak Academy of Sciences
  • María Judith Percino · Víctor Manuel Chapela
    [Show abstract] [Hide abstract] ABSTRACT: The chapter talks about conducting polymers. The doping process is an effective method to produce conducting polymers. Doping allows electrons to flow due to the formation of conduction bands. Electric current is produced when the electrons are moving along the polymer chains. This chapter elaborates on an understanding of the mechanisms of charge storage and charge transfer, the structures and characterization techniques of conducting polymers, and some potential applications for conducting polymers. It also presents some examples of conjugated conducting polymers, including polyacetylene, polypyrrole, polyaniline, and polythiopene.
    No preview · Chapter · Feb 2013
  • [Show abstract] [Hide abstract] ABSTRACT: Four (dimethylamino)arylacrylonitrile derivatives in the solid state are presented. The compounds were characterized by single crystal X-ray diffraction to investigate the effects of substituents on the resulting crystals lattices and to examine the effects of the factors controlling their solid state on photochemical behavior. The molecules included 2-(phenyl)-3-(4-dimethylaminophenyl)acrylonitrile (I) 2-(2′-pyridyl)-3-(4-dimethylaminophenyl)-acrylonitrile (II), 2-(3′-pyridyl)-3-(4-dimethyl-aminophenyl)acrylonitrile (III) and 2-(3′-pyridyl)-3-(4-dimethylaminophenyl)acrylonitrile (IV). The dimethyl-, CN groups and the position of nitrogen atom in the pyridyl groups affected the nature of the molecular packing and consequently their fluorescence properties. The lattice of each compound is compared with acrylonitriles previously reported and the effect of substitution on the crystal properties with the strongest emission in solid state is examined. Based on analyses of molecular packing in the single crystals, the differences in the fluorescence could be attributed to aggregates that showed non-classical herringbone packing with π–π overlap between neighbor molecules. Also the crystal structure studies showed that the N atom position is located anti to the CN group, giving a more planar geometry. This N-dimethyl substituent for I–IV appears to be general for more planar ground-state geometry about the nitrogen atom and consistent with an “amino conjugation effect” to obtain sufficient quinoid structures.
    No preview · Article · Feb 2013 · Journal of Molecular Structure
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    [Show abstract] [Hide abstract] ABSTRACT: A combined theoretical and experimental study on the structure, infrared, UV-Vis and 1H NMR data of trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)]pyridine and trans-4-(m-cyanostyryl)pyridine is presented. The synthesis was carried out with an efficient Knoevenagel condensation using green chemistry conditions. Theoretical geometry optimizations and their IR spectra were carried out using the Density Functional Theory (DFT) in both gas and solution phases. For theoretical UV-Vis and 1H NMR spectra, the Time-Dependent DFT (TD-DFT) and the Gauge-Including Atomic Orbital (GIAO) methods were used, respectively. The theoretical characterization matched the experimental measurements, showing a good correlation. The effect of cyano- and methyl- substituents, as well as of the N-atom position in the pyridine ring on the UV-Vis, IR and NMR spectra, was evaluated. The UV-Vis results showed no significant effect due to electron-withdrawing cyano- and electron-donating methyl-substituents. The N-atom position, however, caused a slight change in the maximum absorption wavelengths. The IR normal modes were assigned for the cyano- and methyl-groups. 1H NMR spectra showed the typical doublet signals due to protons in the trans position of a double bond. The theoretical characterization was visibly useful to assign accurately the signals in IR and 1H NMR spectra, as well as to identify the most probable conformation that could be present in the formation of the styrylpyridine-like compounds.
    Full-text · Article · Feb 2013 · International Journal of Molecular Sciences
  • F. Calvo · F.D. Calvo · V.M. Chapela · M.J. Percino · L. Trinidad
    [Show abstract] [Hide abstract] ABSTRACT: In a conventional design process, several methodologies can be applied to optimize the design; however, these methods may be slow and too dependent on the designeŕs expertise and the project limitations. Furthermore, some methodologies are mainly based on trial and error, thereby making them slow and inaccurate. Many techniques are fundamentally based on the decisions derived from the designer's criteria, such as the specification of what is to be modified (e.g., material, geometry, dimensions). As a result, the final design may not be based on an optimization analysis that leads to a better design. In preparing for a mechanical design, aspects such as shape, dimensions, and topology are analyzed; heavy production demands force the designer to identify new methods and tools that allow him to optimize his work and its results, including the elements, machines, and structures. With the recent development of computational tools, topologic optimization and the finite element method are now possible, among other techniques. This paper presents the use of a finite element method to conduct a topologic optimization using the SolidWorks software, with the goal of optimizing the solar panel thickness in a solar collector.
    No preview · Article · Jan 2013