S. Mekelleche - Academia.edu (original) (raw)

Papers by S. Mekelleche

Research paper thumbnail of A Density Functional Theory Study of the Adsorption of 2-Cyclohexenone on Rh(111)

Advances in Quantum Chemistry, 2014

Research paper thumbnail of Reactivity of pyrrole, furane, and tiophene in electrophilic substitution reactions: A conceptual DFT approach

Les indices de Fukui,qui sont des descripteurs de reactivite derivant de la theorie de la fonctio... more Les indices de Fukui,qui sont des descripteurs de reactivite derivant de la theorie de la fonctionnelle de densite (DFT), sont utilises pour la prediction des sites preferentiels d'attaque electrophile sur les heterocycles a cinq chainons (pyrrole, furanne et thiophene). Les reactivites relatives de ces systemes sont rationalisees par le calcul de la mollesse locale du site le plus reactif dans chaque systeme. 1 es resultats obtenus par cette approche sont en parfait accord avec l'experience.

Research paper thumbnail of Elucidation of the regioselectivity in Diels-Alder reactions by means of theoretical approaches

Journal of Molecular Structure-Theochem, 2004

In this work, we have elucidated the regioselectivity in some Diels–Alder reactions essentially b... more In this work, we have elucidated the regioselectivity in some Diels–Alder reactions essentially by means of the Hard and Soft Acid Base principle applied locally. On the basis of the Gazquez–Mendez conclusions, we calculated the condensed local softnesses for the terminal atoms in order to show the preferential cyclization mode of these reactions. The results obtained with the B3LYP/6-31G* method confirm the ortho regioselectivity observed experimentally. The regioselectivity of these reactions has also been confirmed by the calculation of the activation energies and by the application of the Houk rule.

Research paper thumbnail of Correlation of aqueous pK(a) values of carbon acids with theoretical descriptors: A DFT study

Journal of Molecular Structure-Theochem, 2007

Theoretical calculations are carried out to predict gas-and aqueous-phase acidities of a series o... more Theoretical calculations are carried out to predict gas-and aqueous-phase acidities of a series of 21 carbon acids with pK a values varying from À6.20 to 50. Acceptable linear correlations (R 2 > 0.93, SD < 4) are obtained between calculated deprotonation Gibbs free energy changes and experimental pK a values (measured in water). Solvent effects are taken into account by means of the polarizable continuum model (PCM). Our calculations also show that the high acidity of a-proton carbonyl compounds and electron-withdrawing substituted methanes can be related to the strong increase in the vicinal charge interactions n c fi p * in anion species. Calculations are performed at the B3LYP/6-311++G(d,p) level of theory.

Research paper thumbnail of Elucidation of the substitutent effects on the reaction pathway of the cycloaddition of 1,3-diazabuta-1,3-dienes with ketenes using DFT-based reactivity indexes

Journal of Molecular Structure-Theochem, 2007

ABSTRACT The two possible [2+2] and [4+2] reaction pathways of a series of cycloaddition reaction... more ABSTRACT The two possible [2+2] and [4+2] reaction pathways of a series of cycloaddition reactions of N-substituted 1,3-diazabuta-1,3-dienes with ketenes are elucidated theoretically by means of DFT-based reactivity indexes. In the first step of the stepwise mechanism, the σ-bond formation is rationalized by the determination of the most favorable electrophile–nucleophile interaction using Domingo’s polar model [L.R. Domingo et al., Tetrahedron 58 (2002) 4417]. In the second step – which corresponds to a ring-closure – the formation of either a four- or a six-membered heterocycle is justified by the electrostatic interaction between the more positively and more negatively charged centers of the zwitterionic intermediate. The calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in total agreement with experimental findings.

Research paper thumbnail of Prediction of the reactivity of 2(5H)-furanones as potential dienophiles in Diels-Alder reactions using philicity indexes

Journal of Molecular Structure-Theochem, 2007

The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-fur... more The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-furanones as dienophiles in Diels–Alder reactions. The local reactivity and the preferential cyclization modes of these cycloadditions are predicted using philicity indexes recently proposed by Chattaraj et al. [P.K. Chattaraj, B. Maiti, U. Sarkar, J. Phys. Chem. A 107 (2003) 4973] for the prediction of the

Research paper thumbnail of An Analysis of the Regioselectivity in Hetero Diels–Alder Reactions Using DFT-Based Reactivity Indexes

Journal of Theoretical and Computational Chemistry, 2006

The regioselectivity of hetero Diels–Alder reactions (HDA) of 2-azabutadiene with aldehydes has b... more The regioselectivity of hetero Diels–Alder reactions (HDA) of 2-azabutadiene with aldehydes has been elucidated by means of Gazquez–Mendez rules, which are based on the calculation of local softnesses of the four terminal atoms involved in cyclization. The theoretical results obtained with the B3LYP/6-31G(d) method confirm the regioselectivities observed experimentally for all substituents ( R = H , CH 3, CN ) present in the aldehyde reactant. The regioselectivities of these HDA reactions have been confirmed by the calculation of the activation barriers corresponding to the two cyclization modes, and also by the application of the Houk rule and the maximum hardness principle.

Research paper thumbnail of Influence of substitution of phenyl group by naphthyl in a diphenylthiourea molecule on corrosion inhibition of cold-rolled steel in 0.5 M H2SO4

Journal of Materials Science, 2006

Page 1. Abstract N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized... more Page 1. Abstract N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized in our laboratory, were tested as inhibitors for the corro-sion of cold-rolled steel in 0.5 MH2SO4 by weight loss and electrochemical measurements. ...

Research paper thumbnail of 2-Mercapto-1-methylimidazole as corrosion inhibitor of copper in aerated 3% NaCl solution

Annales de Chimie Science des Matériaux, 2000

Research paper thumbnail of Nonlinear optical activity of imino-dyes with furan, thiophene or thiazole moieties as π-conjugated bridge: a computational investigation

Molecular Physics, 2020

ABSTRACT The electronic, linear and nonlinear optical properties of some heterocycle-containing i... more ABSTRACT The electronic, linear and nonlinear optical properties of some heterocycle-containing imino-dyes, namely, the synthesised dyes 1–3 and the designed dye 4, were evaluated using suitable long-range corrected DFT functionals. HOMO–LUMO gaps, dipole moments, polarisabilities, and first hyperpolarisabilities were calculated using CAM-B3LYP, ωB97XD and LC-ωPBE methods combined with the 6-311++G(d,p) basis set using CAM-B3LYP/6-31G(d,p) optimised geometries. The calculated molecular hyperpolarisabilities, µβ, increase in the order 1 < 2 < 3 as expected experimentally. The enhancement of µβ when passing from dye 1 to dye 2 is due to the replacement of furan by thiophene and the increase of µβ when passing from dye 2 to dye 3 is due to the change of the thiophene position from the acceptor side to the donor side. Interestingly, the replacement of thiophene (dye 2) by thiazole (dye 4) leads to a notable increase of the NLO response. The electronic transitions data of dyes 1–4 were calculated at the CIS/6-31G(d,p) level of theory and the predicted order 1 < 2<3 < 4 of µβ values is conveniently explained using the two-level model based on the calculation of the dipole moment absolute change, |ΔµEG |, from the ground to the excited state. Consequently, dye 4 could be a promising candidate for organic NLO devices. GRAPHICAL ABSTRACT

Research paper thumbnail of Theoretical analysis of the regioselectivity of 1,3-dipolar cycloaddition of C-(methoxycarbonyl)-N-methyl with methyl acrylate and vinyl acetate

Journal of Molecular Structure-Theochem, 2008

ABSTRACT The regioselectivity of 1,3-dipolar cycloaddition of C-(methoxycarbonyl)-N-methyl nitron... more ABSTRACT The regioselectivity of 1,3-dipolar cycloaddition of C-(methoxycarbonyl)-N-methyl nitrone with methyl acrylate and vinyl acetate is analyzed by means of several theoretical approaches, namely, activation energy calculations, FMO theory, and DFT-based reactivity indices. The quantum chemistry calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in agreement with experimental outcomes.

Research paper thumbnail of Theoretical study of the mechanism and regioselectivity of the 1,3-dipolar cycloaddition of diazomethane with methyl acrylate using theoretical approaches

Journal of Molecular Structure THEOCHEM

In this work, the mechanism and regioselectivity of the 1,3-dipolar cycloaddition of diazomethane... more In this work, the mechanism and regioselectivity of the 1,3-dipolar cycloaddition of diazomethane with methyl acrylate are studied using several quantum chemistry approaches. Potential energy surface analysis and IRC calculations show that this cycloaddition follows an asynchronous concerted mechanism through the ortho channel. The favored cyclization mode and the experimental regioselectivity of this cycloaddition are rationalized by both activation energy calculations, FMO model, and philicity indexes derived from density functional theory. The calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in agreement with experimental outcomes.

Research paper thumbnail of Prediction of the reactivity of 2(5H)-furanones as potential dienophiles in Diels-Alder reactions using philicity indexes

Journal of Molecular Structure-Theochem, 2007

The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-fur... more The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-furanones as dienophiles in Diels–Alder reactions. The local reactivity and the preferential cyclization modes of these cycloadditions are predicted using philicity indexes recently proposed by Chattaraj et al. [P.K. Chattaraj, B. Maiti, U. Sarkar, J. Phys. Chem. A 107 (2003) 4973] for the prediction of the

Research paper thumbnail of Reactivity and regioselectivity of five-membered heterocycles in electrophilic aromatic substitution: A theoretical investigation

Journal of Molecular Structure-Theochem, 2010

ABSTRACT

Research paper thumbnail of Unified analytical treatment of one-electron two-center integrals with noninteger n Slater-type orbitals

Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2000

A uni®ed treatment of one-electron twocenter integrals over noninteger n Slater-type orbitals is ... more A uni®ed treatment of one-electron twocenter integrals over noninteger n Slater-type orbitals is described. Using an appropriate prolate spheroidal coordinate system with the two atomic centers as foci, all the molecular integrals are expressed by a single analytical formula which can be readily and compactly programmed. The analysis of the numerical performance of the computational algorithm is also presented.

Research paper thumbnail of SOLVENT EFFECTS ON THE KETO-ENOL TAUTOMERIC EQUILIBRIUM OF TETRONIC AND ETHYL ACETOACETATE CARBON ACIDS: A THEORETICAL STUDY

Journal of Theoretical and Computational Chemistry, 2010

ABSTRACT The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA)... more ABSTRACT The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA) and tetronic acid (TA) are theoretically investigated. The present study shows that the most stable keto tautomer of EAA corresponds to the trans diketo, E, Z form; while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. Our calculations also put in evidence that the keto tautomer of TA prefers the trans diketo, E, E form, while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. The calculated free energies indicate that, in polar solvents, the keto-enol equilibrium of EAA is shifted towards the keto tautomer, whereas the keto-enol equilibrium of TA is shifted toward the enol tautomer. The trends of the change of equilibrium constants with respect to the change of solvent polarity are well reproduced by both B3LYP and MP2 calculations. The present study shows that the enthalpic term is predominant in the determination of the calculated equilibrium constants and the entropic effect on the calculated Gibbs free energies is found to be very small and has little influence on the studied keto-enol tautomeric equilibriums.

Research paper thumbnail of Understanding the kinetic solvent effects on the 1,3-dipolar cycloaddition of benzonitrile N-oxide: a DFT study

Journal of Physical Organic Chemistry, 2011

ABSTRACT The kinetic solvent effects on the 1,3-dipolar cycloaddition (13DC) of benzonitrile N-ox... more ABSTRACT The kinetic solvent effects on the 1,3-dipolar cycloaddition (13DC) of benzonitrile N-oxide with cyclopentene [T. Rispens and J. B. F. N. Engberts, J. Phys. Org. Chem. 2005; 18, 908-917] have been studied using density functional theory (DFT) at the B3LYP/6-31 G(d) level. Solvent effects were analyzed by means of the polarizable continuum model (PCM). The analysis of the potential energy surface shows that this reaction follows an asynchronous concerted mechanism. The topological analysis of the electron localization function (ELF) of the turning points along the reaction pathway explains the diradical nature of mechanism of this reaction. Inclusion of solvent effects does not substantially modify this behavior. The present study points out that, contrary to Diels-Alder reactions, the increase in the solvent polarity leads to a slow inhibition of the 13DC reaction, because of the low polarity of the transition state. Explicit solvation involving the coordination of one water molecule to the dipole puts in evidence the importance of hydrogen bonding in the modest acceleration of this 13DC reaction. These results are in good agreement with experimental outcomes. Copyright (C) 2011 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of Calculation of the one‐electron two‐center integrals over Slater‐type orbitals by means of the ellipsoidal coordinates method

International Journal of Quantum Chemistry, 1997

It is also possible that your web browser is not configured or not able to display style sheets. ... more It is also possible that your web browser is not configured or not able to display style sheets. In this case, although the visual presentation will be degraded, the site should continue to be functional. We recommend using the latest version of Microsoft or Mozilla web browser to ...

Research paper thumbnail of Correlation of aqueous pK(a) values of carbon acids with theoretical descriptors: A DFT study

Journal of Molecular Structure-Theochem, 2007

ABSTRACT Theoretical calculations are carried out to predict gas- and aqueous-phase acidities of ... more ABSTRACT Theoretical calculations are carried out to predict gas- and aqueous-phase acidities of a series of 21 carbon acids with pK(a) values varying from -6.20 to 50. Acceptable linear correlations (R-2 &gt; 0.93, SD &lt; 4) are obtained between calculated deprotonation Gibbs free energy changes and experimental pK(a) values (measured in water). Solvent effects are taken into account by means of the polarizable continuum model (PCM). Our calculations also show that the high acidity of alpha-proton carbonyl compounds and electron-withdrawing substituted methanes can be related to the strong increase in the vicinal charge interactions n(c) -&gt;-pi(*) in anion species. Calculations are perfomed at the B3LYP/6-311++G(d,p) level of theory. (c) 2007 Elsevier B.V. All rights reserved.

Research paper thumbnail of A Density Functional Theory Study of the Adsorption of 2-Cyclohexenone on Rh(111)

Advances in Quantum Chemistry, 2014

Research paper thumbnail of Reactivity of pyrrole, furane, and tiophene in electrophilic substitution reactions: A conceptual DFT approach

Les indices de Fukui,qui sont des descripteurs de reactivite derivant de la theorie de la fonctio... more Les indices de Fukui,qui sont des descripteurs de reactivite derivant de la theorie de la fonctionnelle de densite (DFT), sont utilises pour la prediction des sites preferentiels d'attaque electrophile sur les heterocycles a cinq chainons (pyrrole, furanne et thiophene). Les reactivites relatives de ces systemes sont rationalisees par le calcul de la mollesse locale du site le plus reactif dans chaque systeme. 1 es resultats obtenus par cette approche sont en parfait accord avec l'experience.

Research paper thumbnail of Elucidation of the regioselectivity in Diels-Alder reactions by means of theoretical approaches

Journal of Molecular Structure-Theochem, 2004

In this work, we have elucidated the regioselectivity in some Diels–Alder reactions essentially b... more In this work, we have elucidated the regioselectivity in some Diels–Alder reactions essentially by means of the Hard and Soft Acid Base principle applied locally. On the basis of the Gazquez–Mendez conclusions, we calculated the condensed local softnesses for the terminal atoms in order to show the preferential cyclization mode of these reactions. The results obtained with the B3LYP/6-31G* method confirm the ortho regioselectivity observed experimentally. The regioselectivity of these reactions has also been confirmed by the calculation of the activation energies and by the application of the Houk rule.

Research paper thumbnail of Correlation of aqueous pK(a) values of carbon acids with theoretical descriptors: A DFT study

Journal of Molecular Structure-Theochem, 2007

Theoretical calculations are carried out to predict gas-and aqueous-phase acidities of a series o... more Theoretical calculations are carried out to predict gas-and aqueous-phase acidities of a series of 21 carbon acids with pK a values varying from À6.20 to 50. Acceptable linear correlations (R 2 > 0.93, SD < 4) are obtained between calculated deprotonation Gibbs free energy changes and experimental pK a values (measured in water). Solvent effects are taken into account by means of the polarizable continuum model (PCM). Our calculations also show that the high acidity of a-proton carbonyl compounds and electron-withdrawing substituted methanes can be related to the strong increase in the vicinal charge interactions n c fi p * in anion species. Calculations are performed at the B3LYP/6-311++G(d,p) level of theory.

Research paper thumbnail of Elucidation of the substitutent effects on the reaction pathway of the cycloaddition of 1,3-diazabuta-1,3-dienes with ketenes using DFT-based reactivity indexes

Journal of Molecular Structure-Theochem, 2007

ABSTRACT The two possible [2+2] and [4+2] reaction pathways of a series of cycloaddition reaction... more ABSTRACT The two possible [2+2] and [4+2] reaction pathways of a series of cycloaddition reactions of N-substituted 1,3-diazabuta-1,3-dienes with ketenes are elucidated theoretically by means of DFT-based reactivity indexes. In the first step of the stepwise mechanism, the σ-bond formation is rationalized by the determination of the most favorable electrophile–nucleophile interaction using Domingo’s polar model [L.R. Domingo et al., Tetrahedron 58 (2002) 4417]. In the second step – which corresponds to a ring-closure – the formation of either a four- or a six-membered heterocycle is justified by the electrostatic interaction between the more positively and more negatively charged centers of the zwitterionic intermediate. The calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in total agreement with experimental findings.

Research paper thumbnail of Prediction of the reactivity of 2(5H)-furanones as potential dienophiles in Diels-Alder reactions using philicity indexes

Journal of Molecular Structure-Theochem, 2007

The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-fur... more The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-furanones as dienophiles in Diels–Alder reactions. The local reactivity and the preferential cyclization modes of these cycloadditions are predicted using philicity indexes recently proposed by Chattaraj et al. [P.K. Chattaraj, B. Maiti, U. Sarkar, J. Phys. Chem. A 107 (2003) 4973] for the prediction of the

Research paper thumbnail of An Analysis of the Regioselectivity in Hetero Diels–Alder Reactions Using DFT-Based Reactivity Indexes

Journal of Theoretical and Computational Chemistry, 2006

The regioselectivity of hetero Diels–Alder reactions (HDA) of 2-azabutadiene with aldehydes has b... more The regioselectivity of hetero Diels–Alder reactions (HDA) of 2-azabutadiene with aldehydes has been elucidated by means of Gazquez–Mendez rules, which are based on the calculation of local softnesses of the four terminal atoms involved in cyclization. The theoretical results obtained with the B3LYP/6-31G(d) method confirm the regioselectivities observed experimentally for all substituents ( R = H , CH 3, CN ) present in the aldehyde reactant. The regioselectivities of these HDA reactions have been confirmed by the calculation of the activation barriers corresponding to the two cyclization modes, and also by the application of the Houk rule and the maximum hardness principle.

Research paper thumbnail of Influence of substitution of phenyl group by naphthyl in a diphenylthiourea molecule on corrosion inhibition of cold-rolled steel in 0.5 M H2SO4

Journal of Materials Science, 2006

Page 1. Abstract N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized... more Page 1. Abstract N,N′-Diphenylthiourea (DPTU) and N-naphthyl-N′-phenylthiourea (NPTU) synthesized in our laboratory, were tested as inhibitors for the corro-sion of cold-rolled steel in 0.5 MH2SO4 by weight loss and electrochemical measurements. ...

Research paper thumbnail of 2-Mercapto-1-methylimidazole as corrosion inhibitor of copper in aerated 3% NaCl solution

Annales de Chimie Science des Matériaux, 2000

Research paper thumbnail of Nonlinear optical activity of imino-dyes with furan, thiophene or thiazole moieties as π-conjugated bridge: a computational investigation

Molecular Physics, 2020

ABSTRACT The electronic, linear and nonlinear optical properties of some heterocycle-containing i... more ABSTRACT The electronic, linear and nonlinear optical properties of some heterocycle-containing imino-dyes, namely, the synthesised dyes 1–3 and the designed dye 4, were evaluated using suitable long-range corrected DFT functionals. HOMO–LUMO gaps, dipole moments, polarisabilities, and first hyperpolarisabilities were calculated using CAM-B3LYP, ωB97XD and LC-ωPBE methods combined with the 6-311++G(d,p) basis set using CAM-B3LYP/6-31G(d,p) optimised geometries. The calculated molecular hyperpolarisabilities, µβ, increase in the order 1 < 2 < 3 as expected experimentally. The enhancement of µβ when passing from dye 1 to dye 2 is due to the replacement of furan by thiophene and the increase of µβ when passing from dye 2 to dye 3 is due to the change of the thiophene position from the acceptor side to the donor side. Interestingly, the replacement of thiophene (dye 2) by thiazole (dye 4) leads to a notable increase of the NLO response. The electronic transitions data of dyes 1–4 were calculated at the CIS/6-31G(d,p) level of theory and the predicted order 1 < 2<3 < 4 of µβ values is conveniently explained using the two-level model based on the calculation of the dipole moment absolute change, |ΔµEG |, from the ground to the excited state. Consequently, dye 4 could be a promising candidate for organic NLO devices. GRAPHICAL ABSTRACT

Research paper thumbnail of Theoretical analysis of the regioselectivity of 1,3-dipolar cycloaddition of C-(methoxycarbonyl)-N-methyl with methyl acrylate and vinyl acetate

Journal of Molecular Structure-Theochem, 2008

ABSTRACT The regioselectivity of 1,3-dipolar cycloaddition of C-(methoxycarbonyl)-N-methyl nitron... more ABSTRACT The regioselectivity of 1,3-dipolar cycloaddition of C-(methoxycarbonyl)-N-methyl nitrone with methyl acrylate and vinyl acetate is analyzed by means of several theoretical approaches, namely, activation energy calculations, FMO theory, and DFT-based reactivity indices. The quantum chemistry calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in agreement with experimental outcomes.

Research paper thumbnail of Theoretical study of the mechanism and regioselectivity of the 1,3-dipolar cycloaddition of diazomethane with methyl acrylate using theoretical approaches

Journal of Molecular Structure THEOCHEM

In this work, the mechanism and regioselectivity of the 1,3-dipolar cycloaddition of diazomethane... more In this work, the mechanism and regioselectivity of the 1,3-dipolar cycloaddition of diazomethane with methyl acrylate are studied using several quantum chemistry approaches. Potential energy surface analysis and IRC calculations show that this cycloaddition follows an asynchronous concerted mechanism through the ortho channel. The favored cyclization mode and the experimental regioselectivity of this cycloaddition are rationalized by both activation energy calculations, FMO model, and philicity indexes derived from density functional theory. The calculations are performed at the B3LYP/6-31G(d) level of theory and the obtained results are in agreement with experimental outcomes.

Research paper thumbnail of Prediction of the reactivity of 2(5H)-furanones as potential dienophiles in Diels-Alder reactions using philicity indexes

Journal of Molecular Structure-Theochem, 2007

The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-fur... more The global electrophilicity index is used for classifying the reactivity of a series of 2(5H)-furanones as dienophiles in Diels–Alder reactions. The local reactivity and the preferential cyclization modes of these cycloadditions are predicted using philicity indexes recently proposed by Chattaraj et al. [P.K. Chattaraj, B. Maiti, U. Sarkar, J. Phys. Chem. A 107 (2003) 4973] for the prediction of the

Research paper thumbnail of Reactivity and regioselectivity of five-membered heterocycles in electrophilic aromatic substitution: A theoretical investigation

Journal of Molecular Structure-Theochem, 2010

ABSTRACT

Research paper thumbnail of Unified analytical treatment of one-electron two-center integrals with noninteger n Slater-type orbitals

Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta), 2000

A uni®ed treatment of one-electron twocenter integrals over noninteger n Slater-type orbitals is ... more A uni®ed treatment of one-electron twocenter integrals over noninteger n Slater-type orbitals is described. Using an appropriate prolate spheroidal coordinate system with the two atomic centers as foci, all the molecular integrals are expressed by a single analytical formula which can be readily and compactly programmed. The analysis of the numerical performance of the computational algorithm is also presented.

Research paper thumbnail of SOLVENT EFFECTS ON THE KETO-ENOL TAUTOMERIC EQUILIBRIUM OF TETRONIC AND ETHYL ACETOACETATE CARBON ACIDS: A THEORETICAL STUDY

Journal of Theoretical and Computational Chemistry, 2010

ABSTRACT The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA)... more ABSTRACT The solvent effects on the keto-enol tautomeric equilibriums of ethyl acetoacetate (EAA) and tetronic acid (TA) are theoretically investigated. The present study shows that the most stable keto tautomer of EAA corresponds to the trans diketo, E, Z form; while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. Our calculations also put in evidence that the keto tautomer of TA prefers the trans diketo, E, E form, while the most stable enol tautomer corresponds to the structure in which the enolization takes place at the carbonyl group. The calculated free energies indicate that, in polar solvents, the keto-enol equilibrium of EAA is shifted towards the keto tautomer, whereas the keto-enol equilibrium of TA is shifted toward the enol tautomer. The trends of the change of equilibrium constants with respect to the change of solvent polarity are well reproduced by both B3LYP and MP2 calculations. The present study shows that the enthalpic term is predominant in the determination of the calculated equilibrium constants and the entropic effect on the calculated Gibbs free energies is found to be very small and has little influence on the studied keto-enol tautomeric equilibriums.

Research paper thumbnail of Understanding the kinetic solvent effects on the 1,3-dipolar cycloaddition of benzonitrile N-oxide: a DFT study

Journal of Physical Organic Chemistry, 2011

ABSTRACT The kinetic solvent effects on the 1,3-dipolar cycloaddition (13DC) of benzonitrile N-ox... more ABSTRACT The kinetic solvent effects on the 1,3-dipolar cycloaddition (13DC) of benzonitrile N-oxide with cyclopentene [T. Rispens and J. B. F. N. Engberts, J. Phys. Org. Chem. 2005; 18, 908-917] have been studied using density functional theory (DFT) at the B3LYP/6-31 G(d) level. Solvent effects were analyzed by means of the polarizable continuum model (PCM). The analysis of the potential energy surface shows that this reaction follows an asynchronous concerted mechanism. The topological analysis of the electron localization function (ELF) of the turning points along the reaction pathway explains the diradical nature of mechanism of this reaction. Inclusion of solvent effects does not substantially modify this behavior. The present study points out that, contrary to Diels-Alder reactions, the increase in the solvent polarity leads to a slow inhibition of the 13DC reaction, because of the low polarity of the transition state. Explicit solvation involving the coordination of one water molecule to the dipole puts in evidence the importance of hydrogen bonding in the modest acceleration of this 13DC reaction. These results are in good agreement with experimental outcomes. Copyright (C) 2011 John Wiley &amp; Sons, Ltd.

Research paper thumbnail of Calculation of the one‐electron two‐center integrals over Slater‐type orbitals by means of the ellipsoidal coordinates method

International Journal of Quantum Chemistry, 1997

It is also possible that your web browser is not configured or not able to display style sheets. ... more It is also possible that your web browser is not configured or not able to display style sheets. In this case, although the visual presentation will be degraded, the site should continue to be functional. We recommend using the latest version of Microsoft or Mozilla web browser to ...

Research paper thumbnail of Correlation of aqueous pK(a) values of carbon acids with theoretical descriptors: A DFT study

Journal of Molecular Structure-Theochem, 2007

ABSTRACT Theoretical calculations are carried out to predict gas- and aqueous-phase acidities of ... more ABSTRACT Theoretical calculations are carried out to predict gas- and aqueous-phase acidities of a series of 21 carbon acids with pK(a) values varying from -6.20 to 50. Acceptable linear correlations (R-2 &gt; 0.93, SD &lt; 4) are obtained between calculated deprotonation Gibbs free energy changes and experimental pK(a) values (measured in water). Solvent effects are taken into account by means of the polarizable continuum model (PCM). Our calculations also show that the high acidity of alpha-proton carbonyl compounds and electron-withdrawing substituted methanes can be related to the strong increase in the vicinal charge interactions n(c) -&gt;-pi(*) in anion species. Calculations are perfomed at the B3LYP/6-311++G(d,p) level of theory. (c) 2007 Elsevier B.V. All rights reserved.