Tania C Cordova-Sintjago | Santa Fe College (original) (raw)

Papers by Tania C Cordova-Sintjago

Research paper thumbnail of Molecular Pharmacology and Ligand Docking Studies Reveal a Single Amino Acid Difference between Mouse and Human Serotonin 5-HT2A Receptors That Impacts Behavioral Translation of Novel 4-Phenyl-2-dimethylaminotetralin Ligands

Journal of Pharmacology and Experimental Therapeutics, 2013

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Research paper thumbnail of Sulfonylation of Five‐Membered Aromatic Heterocycles Compounds through Nucleophilic Aromatic Substitution: Concerted or Stepwise Mechanism?

ChemistrySelect, Apr 17, 2020

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Research paper thumbnail of Kinetics and mechanism for oxime formation from 4-dimethylaminobenzaldehyde and 4-trimethylammoniobenzaldehyde iodide

International Journal of Chemical Kinetics, 1999

The following lines of evidence establish that oxime formation from 4-dimethylaminobenzaldehyde a... more The following lines of evidence establish that oxime formation from 4-dimethylaminobenzaldehyde and 4-trimethylammoniobenzaldehyde iodide occurs with a simple two-step mechanism. The pH-rate profile for the reaction of 4-trimethylammoniobenzaldehyde iodide exhibits, in order of decreasing pH, a negative deviation at pH near 2.0, corresponding to a transition from rate-determining step carbinolamine dehydration with acid catalysis to the uncatalyzed carbinolamine formation. In the case of the reaction of 4-dimethylaminobenzaldehyde, the pH-profile exhibits, in order of decreasing pH, a positive deviation at pH near 3.5 and then a negative deviation at pH near 2.0. These deviations have been interpreted in terms of i) transition of the rate-determining step, and ii) protolytic equilibrium of the substrate. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 387–392, 1999

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Research paper thumbnail of Kinetic Determination of the Gas-Phase Decarbonylation of Butyraldehyde in the Presence of HCl Catalyst

International Journal of Chemical Kinetics, Mar 15, 2017

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Research paper thumbnail of Kinetics and Mechanisms of the Thermal Decomposition of 2-Methyl-1,3-dioxolane, 2,2-Dimethyl-1,3-dioxolane, and Cyclopentanone Ethylene Ketal in the Gas Phase. Combined Experimental and DFT Study

Journal of Physical Chemistry A, Sep 4, 2012

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Research paper thumbnail of Kinetics and mechanism for oxime formation from methyl pyruvate

Journal of Physical Organic Chemistry, Dec 7, 2001

Rate and equilibrium constants for methyl pyruvate oxime formation were determined as a function ... more Rate and equilibrium constants for methyl pyruvate oxime formation were determined as a function of pH over the range 0–7 in aqueous solution at 30 °C and ionic strength 0.5 by spectrophotometric methods. The reaction occurs with rate‐determining carbinolamine dehydration over the entire range of pH investigated. Carbinolamine dehydration is not susceptible to detectable general acid–base catalysis by a carboxylic acid buffer or hydroxylamine/hydroxylammonium ion buffer. Specific acid catalysis for carbinolamine formation is dominant at­pH values below 5. Above that value, a pH‐independent, water‐catalyzed reaction becomes apparent. The­pH‐independent carbinolamine dehydration is unusually important with this substrate. Copyright © 2001 John Wiley & Sons, Ltd.

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Research paper thumbnail of Reaction Mechanism of the Gas-Phase Pyrolysis of N – Acetylthiourea and N, N’–Diacetylthiourea: A Theoretical Study Based in Density Functional Theory

Social Science Research Network, 2022

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Research paper thumbnail of Experimental and theoretical study of the mechanism for the kinetic of elimination of methyl carbazate in the gas phase

Journal of Physical Organic Chemistry, Feb 1, 2009

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Research paper thumbnail of Density functional theory andab initiostudy on the reaction mechanisms of the homogeneous, unimolecular elimination kinetics of selected 1-chloroalkenes in the gas phase

International Journal of Quantum Chemistry, May 24, 2012

ABSTRACT The mechanisms for the unimolecular elimination kinetics of selected 1-chloroalkenes in ... more ABSTRACT The mechanisms for the unimolecular elimination kinetics of selected 1-chloroalkenes in the gas phase were studied at MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), G3, and G3MP2 levels of theory. Two possible unimolecular mechanisms were considered: mechanism A as a concerted 1,2 elimination process through four-membered cyclic transition state (TS). mechanism B describing the anchimeric assistance of the double bond in HCl elimination previously suggested in the literature. Calculated parameters suggest that the elimination reactions of 1-chloroalkenes proceed through mechanism A, in view of the higher energy of activation associated with mechanism B. Density functional method MPW1PW91/6-31G(d,p) calculated parameters gave a better agreement with the experimental values than G3 and G3MP2. The changes along the reaction path of mechanism A were followed by geometric parameters, natural bond orbital charges, and bond order analysis, suggesting the rate-determining process is the breaking of CCl bond in the TS. The dehydrochlorination of chloroalkenes occurs in a concerted nonsynchronous fashion with stabilization of the TS by π-electron delocalization from the neighboring bond. Isomerization reactions for 4-chloro-1-butene, 4-chloro-2-methyl-1-butene, and 4-chloro-1-butene are unlikely at the experimental reaction condition because of the higher the enthalpies and energies of activation. © 2012 Wiley Periodicals, Inc.

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Research paper thumbnail of Quantum chemical theory calculations on the mechanism of the homogeneous, unimolecular gas-phase elimination kinetics of selected diazirines

Computational and Theoretical Chemistry, Feb 1, 2016

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Research paper thumbnail of <i>Ab initio</i> and DFT calculations on the gas phase elimination kinetics of 2,2-diethoxy-ethylamine and 2,2-diethoxy-<i>N</i> ,<i>N</i> -diethyl-ethylamine

Journal of Physical Organic Chemistry, Sep 22, 2008

The mechanisms for the gas phase molecular elimination kinetics of 2,2‐diethoxy‐ethylamine and 2,... more The mechanisms for the gas phase molecular elimination kinetics of 2,2‐diethoxy‐ethylamine and 2,2‐diethoxy‐N,N‐diethyl‐ethylamine were examined at MP2/6‐31G, B3LYP/6‐31G, B3LYP/6‐31G(d,p), MPW91PW91/6‐31G. MPW91PW91/6‐31G(d,p), PBEPBE/6‐31G, and PBEPBE/6‐31G(d,p) levels of theory. These elimination processes involve two parallel reactions. The first parallel reaction gives ethanol and the corresponding 2‐ethoxyethenamine. The latter compound further decomposes to ethylene, CO, and the corresponding amine. The second parallel reaction produces ethane and the corresponding ethyl ester of an α‐amino acid. Calculated thermodynamic and kinetic parameters from PBEPBE calculations were found to be in good agreement with the experimental values. The transition states of the parallel reactions are best described as four‐membered cyclic structures. The intermediate 2‐ethoxy‐ethenamine undergoes a consecutive elimination through a six‐membered cyclic transition state mechanism. Bond indexes and synchronicity (Sy) parameters are in agreement with concerted semi‐polar transition state structures. Copyright © 2008 John Wiley &amp; Sons, Ltd.

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Research paper thumbnail of Theoretical calculations on the mechanism of the elimination kinetics of allyl cyclohexyl-, -amine, -sulfide, -ether, and allyl ethyl ether in the gas phase

Computational and Theoretical Chemistry, 2016

Abstract The mechanism of the gas-phase elimination allyl cyclohexyl amine, allyl cyclohexyl sulf... more Abstract The mechanism of the gas-phase elimination allyl cyclohexyl amine, allyl cyclohexyl sulfide, allyl cyclohexyl ether, and allyl ethyl ether has been studied by using ab initio combined methods CBS-QB3, and Density Functional Theory CAM-B3LYP, MPW1PW91, PBE1PBE, M06, and M062X. Products formation is described below: Theoretical calculations of these reactions support the unimolecular process of these gas-phase eliminations. These thermal decompositions undergo a retro-ene type of mechanism and proceed through a non-planar concerted six-membered cyclic transition structure. The energy of activation follow the order allyl ethyl ether (187.0 kJ/mol) > N-allyl cyclohexyl amine (171.7 kJ/mol) > allyl cyclohexyl ether (170.5 kJ/mol) > allyl cyclohexyl sulfide (137.9 kJ/mol). The polarization of C5–Z6 bond, and the electronegativity of the heteroatom (O, N) increases the reaction rate compared to allyl ethyl ether. Conversely, the S atom is positively charged and its electronic effect causes a high dissymmetry in the TS geometry, which appear to accelerate the decomposition. The rate determining step of these substrates is the change in hybridization from sp3 to sp2 reflected in the bond order in C3–C4. Calculated kinetic and thermodynamic parameters from the M06/6-311++G(d,p) level of theory are in reasonable good agreement with the experimental values.

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Research paper thumbnail of Inquiry of the reaction paths in thermal retro-Diels–Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

Computational and Theoretical Chemistry, 2015

Abstract The mechanisms of the thermal decomposition of cyclohexene (CH), 4-methylcyclohexene (4M... more Abstract The mechanisms of the thermal decomposition of cyclohexene (CH), 4-methylcyclohexene (4MCH) and 4-vinyl cyclohexene (4VCH) in the gas-phase were studied by means of electronic structure calculations using perturbation MP2 and Density Functional Theory (DFT) methods. Molecular and diradical reaction pathways were calculated. In the case of the 4-susbstituted cyclohexenes two diradical processes were considered. DFT functionals, including a PT2 correction to the correlation energy, gave reasonable results for all reaction paths considered. Calculated parameters obtained with B2PLYP/6-31+G(d,p) are in good agreement with those reported in Tsang’s experimental study. Evaluated kinetic parameters indicate that CH, 4MCH, and 4VCH should follow the concerted molecular reaction pathway. However, it is possible that a fraction of the reactant molecules could overcome the energy barrier for the radical pathway, because of the high temperatures employed in the experimental conditions. The presence of methyl group in 4MCH slightly favors the breaking of C3 C4 bond. The effect of vinyl group is more dramatic, consisted with a resonance effect stabilizing C3 throughout the bond breaking process. NBO charges suggest these processes are discretely polar, since there are slight variations in the electron density along the reaction coordinates. The analysis of the evolution percentages obtained from bond indexes suggests that these reactions are non-synchronous.

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Research paper thumbnail of DFT and ab-initio study on the mechanism of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their isomerization

Journal of Computational Methods in Sciences and Engineering, 2012

The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3... more The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their interconversion have been examined at MP2 and DFT levels of theory. These halide substrates yield isoprene and hydrogen chloride. The results MPW1PW91 calculations agree with the experimental kinetic parameters showing the elimination reaction occurs at greater rate for 1-chloro-3-methylbut-2-ene than that for the 3-chloro-3-methylbut-1-ene isomer. The mechanism for the molecular elimination of 1-chloro-3-methylbut-2-ene suggests proceeding through an uncommon six-membered cyclic transition state for alkyl halides in the gas phase, while 3-chloro-3-methylbut-1-ene eliminates through the usual four-membered cyclic transition state. The elongation and subsequent polarization of the C-Cl bond, in the direction of C^{δ+}…Cl^{δ-}, is rate determining step of these reactions. The isomerization of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene was additionally studied. The 1-chloro-3-methylbut-2-ene converts to 3-chloro-3-methylbut-1-ene easier than the reverse reaction. This means that 1-chloro-3-methylbut-2-ene was found thermodynamically more stable than 3-chloro-3-methylbut-1-ene.

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Research paper thumbnail of The thermal decomposition of 4-bromobutyric acid in the gas phase: A quantum chemical theory calculation

Journal of Computational Methods in Sciences and Engineering, 2012

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Research paper thumbnail of Development of novel serotonin 7‐targeting compounds based on the 2‐dimethylaminotetralin scaffold (1059.13)

The FASEB Journal, 2014

The serotonin (5-HT) 7 G protein-coupled receptor (GPCR) is the most recent 5-HT receptor cloned,... more The serotonin (5-HT) 7 G protein-coupled receptor (GPCR) is the most recent 5-HT receptor cloned, and is expressed in both the periphery and the CNS. Reports propose 5-HT7 receptors are involved in a wide range of CNS functions, including modulation of circadian rhythms, sleep, pain, body temperature, and cognition. 5-HT7 receptors couple to Gαs, leading to activation of adenylyl cyclases and production of cAMP. Due to paucity of available, selective 5-HT7 ligands, the complexity of CNS processes and to a limited number of studies examining 5-HT7, however, there is no consensus about 5-HT7 receptor CNS neuropharmacological function. We have begun an iterative 5-HT7 receptor structure-based ligand synthesis program to develop novel 5-HT7-targeting phenylaminotetralin (PAT) compounds. A molecular model of the 5-HT7 receptor was built by homology to the recently reported structure of the 5-HT1B GPCR, and computational ligand docking studies were undertaken. Computational results were validated by experimenta...

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Research paper thumbnail of Theoretical study on the mechanism of the gas-phase elimination kinetics of alkyl chloroformates

Molecular Physics, 2015

ABSTRACT The theoretical calculations on the mechanism of the homogeneous and unimolecular gas-ph... more ABSTRACT The theoretical calculations on the mechanism of the homogeneous and unimolecular gas-phase elimination kinetics of alkyl chloroformates– ethyl chloroformate (ECF), isopropyl chloroformate (ICF), and sec-butyl chloroformate (SCF) – have been carried out by using CBS-QB3 level of theory and density functional theory (DFT) functionals CAM-B3LYP, M06, MPW1PW91, and PBE1PBE with the basis sets 6-311++G(d,p) and 6-311++G(2d,2p). The chlorofomate compounds with alkyl ester Cβ–H bond undergo thermal decomposition producing the corresponding olefin, HCl and CO2. These homogeneous eliminations are proposed to undergo two different types of mechanisms: a concerted process, or via the formation of an unstable intermediate chloroformic acid (ClCOOH), which rapidly decomposes to HCl and CO2 gas. Since both elimination mechanisms may occur through a six-membered cyclic transition state structure, it is difficult to elucidate experimentally which is the most reasonable reaction mechanism. Theoretical calculations show that the stepwise mechanism with the formation of the unstable intermediate chloroformic acid from ECF, ICF, and SCF is favoured over one-step elimination. Reasonable agreements were found between theoretical and experimental values at the CAM-B3LYP/6-311++G(d,p) level. GRAPHICAL ABSTRACT

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Research paper thumbnail of Effect of structure on reactivity in oxime formation of benzaldehydes

Journal of Physical Organic Chemistry, 1999

... How to Cite. Calzadilla, M., Malpica, A. and Cordova, T. (1999), Effect of structure on react... more ... How to Cite. Calzadilla, M., Malpica, A. and Cordova, T. (1999), Effect of structure on reactivity in oxime formation of benzaldehydes. ... Author Information. Escuela de Quimica, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, 47102, Venezuela. ...

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Research paper thumbnail of Kinetics and mechanism for oxime formation from benzoylformic acid: Electrostatic interactions in the dehydration of carbinolamines

International Journal of Chemical Kinetics, 2008

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Research paper thumbnail of Efecto de la naringenina, hesperetina y sus formas glicosidadas sobre la replicación de la cepa 17D del virus de la fiebre amarilla

Infections produced by flaviviruses are threats to public health worldwide. The absence of effect... more Infections produced by flaviviruses are threats to public health worldwide. The absence of effective drugs treatment makes imperative the quest for efficient antivirals. Using a plaque inhibition assay we studied the antiviral action of the non-cytotoxic flavanones naringenin, hesperetin, and their glycoside forms on the replication of the 17D strain of yellow fever virus (YFV17D). Using plaque assay the glycosylated forms did not show antiviral effect at the highest concentration used, naringenin and hesperetin reduced the plaque size and the infectious titer up to 85.51% and 100% respectively at the maximum concentration employed. The effective dose (ED 50 ) of naringenin (0.0013 uM), calculated by plaque assay, was approximately tenfold lower than hesperetin (ED 50 0.01 uM), and neither showed any virucidal effect. Evaluation of kinetic entrance of YFV to cell showed that after 2h of infection 80% of the virus was already into the cell, but in the presence of naringenin or hesper...

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Research paper thumbnail of Molecular Pharmacology and Ligand Docking Studies Reveal a Single Amino Acid Difference between Mouse and Human Serotonin 5-HT2A Receptors That Impacts Behavioral Translation of Novel 4-Phenyl-2-dimethylaminotetralin Ligands

Journal of Pharmacology and Experimental Therapeutics, 2013

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Research paper thumbnail of Sulfonylation of Five‐Membered Aromatic Heterocycles Compounds through Nucleophilic Aromatic Substitution: Concerted or Stepwise Mechanism?

ChemistrySelect, Apr 17, 2020

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Research paper thumbnail of Kinetics and mechanism for oxime formation from 4-dimethylaminobenzaldehyde and 4-trimethylammoniobenzaldehyde iodide

International Journal of Chemical Kinetics, 1999

The following lines of evidence establish that oxime formation from 4-dimethylaminobenzaldehyde a... more The following lines of evidence establish that oxime formation from 4-dimethylaminobenzaldehyde and 4-trimethylammoniobenzaldehyde iodide occurs with a simple two-step mechanism. The pH-rate profile for the reaction of 4-trimethylammoniobenzaldehyde iodide exhibits, in order of decreasing pH, a negative deviation at pH near 2.0, corresponding to a transition from rate-determining step carbinolamine dehydration with acid catalysis to the uncatalyzed carbinolamine formation. In the case of the reaction of 4-dimethylaminobenzaldehyde, the pH-profile exhibits, in order of decreasing pH, a positive deviation at pH near 3.5 and then a negative deviation at pH near 2.0. These deviations have been interpreted in terms of i) transition of the rate-determining step, and ii) protolytic equilibrium of the substrate. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 387–392, 1999

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Research paper thumbnail of Kinetic Determination of the Gas-Phase Decarbonylation of Butyraldehyde in the Presence of HCl Catalyst

International Journal of Chemical Kinetics, Mar 15, 2017

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Research paper thumbnail of Kinetics and Mechanisms of the Thermal Decomposition of 2-Methyl-1,3-dioxolane, 2,2-Dimethyl-1,3-dioxolane, and Cyclopentanone Ethylene Ketal in the Gas Phase. Combined Experimental and DFT Study

Journal of Physical Chemistry A, Sep 4, 2012

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Research paper thumbnail of Kinetics and mechanism for oxime formation from methyl pyruvate

Journal of Physical Organic Chemistry, Dec 7, 2001

Rate and equilibrium constants for methyl pyruvate oxime formation were determined as a function ... more Rate and equilibrium constants for methyl pyruvate oxime formation were determined as a function of pH over the range 0–7 in aqueous solution at 30 °C and ionic strength 0.5 by spectrophotometric methods. The reaction occurs with rate‐determining carbinolamine dehydration over the entire range of pH investigated. Carbinolamine dehydration is not susceptible to detectable general acid–base catalysis by a carboxylic acid buffer or hydroxylamine/hydroxylammonium ion buffer. Specific acid catalysis for carbinolamine formation is dominant at­pH values below 5. Above that value, a pH‐independent, water‐catalyzed reaction becomes apparent. The­pH‐independent carbinolamine dehydration is unusually important with this substrate. Copyright © 2001 John Wiley &amp; Sons, Ltd.

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Research paper thumbnail of Reaction Mechanism of the Gas-Phase Pyrolysis of N – Acetylthiourea and N, N’–Diacetylthiourea: A Theoretical Study Based in Density Functional Theory

Social Science Research Network, 2022

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Research paper thumbnail of Experimental and theoretical study of the mechanism for the kinetic of elimination of methyl carbazate in the gas phase

Journal of Physical Organic Chemistry, Feb 1, 2009

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Research paper thumbnail of Density functional theory andab initiostudy on the reaction mechanisms of the homogeneous, unimolecular elimination kinetics of selected 1-chloroalkenes in the gas phase

International Journal of Quantum Chemistry, May 24, 2012

ABSTRACT The mechanisms for the unimolecular elimination kinetics of selected 1-chloroalkenes in ... more ABSTRACT The mechanisms for the unimolecular elimination kinetics of selected 1-chloroalkenes in the gas phase were studied at MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), G3, and G3MP2 levels of theory. Two possible unimolecular mechanisms were considered: mechanism A as a concerted 1,2 elimination process through four-membered cyclic transition state (TS). mechanism B describing the anchimeric assistance of the double bond in HCl elimination previously suggested in the literature. Calculated parameters suggest that the elimination reactions of 1-chloroalkenes proceed through mechanism A, in view of the higher energy of activation associated with mechanism B. Density functional method MPW1PW91/6-31G(d,p) calculated parameters gave a better agreement with the experimental values than G3 and G3MP2. The changes along the reaction path of mechanism A were followed by geometric parameters, natural bond orbital charges, and bond order analysis, suggesting the rate-determining process is the breaking of CCl bond in the TS. The dehydrochlorination of chloroalkenes occurs in a concerted nonsynchronous fashion with stabilization of the TS by π-electron delocalization from the neighboring bond. Isomerization reactions for 4-chloro-1-butene, 4-chloro-2-methyl-1-butene, and 4-chloro-1-butene are unlikely at the experimental reaction condition because of the higher the enthalpies and energies of activation. © 2012 Wiley Periodicals, Inc.

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Research paper thumbnail of Quantum chemical theory calculations on the mechanism of the homogeneous, unimolecular gas-phase elimination kinetics of selected diazirines

Computational and Theoretical Chemistry, Feb 1, 2016

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Research paper thumbnail of <i>Ab initio</i> and DFT calculations on the gas phase elimination kinetics of 2,2-diethoxy-ethylamine and 2,2-diethoxy-<i>N</i> ,<i>N</i> -diethyl-ethylamine

Journal of Physical Organic Chemistry, Sep 22, 2008

The mechanisms for the gas phase molecular elimination kinetics of 2,2‐diethoxy‐ethylamine and 2,... more The mechanisms for the gas phase molecular elimination kinetics of 2,2‐diethoxy‐ethylamine and 2,2‐diethoxy‐N,N‐diethyl‐ethylamine were examined at MP2/6‐31G, B3LYP/6‐31G, B3LYP/6‐31G(d,p), MPW91PW91/6‐31G. MPW91PW91/6‐31G(d,p), PBEPBE/6‐31G, and PBEPBE/6‐31G(d,p) levels of theory. These elimination processes involve two parallel reactions. The first parallel reaction gives ethanol and the corresponding 2‐ethoxyethenamine. The latter compound further decomposes to ethylene, CO, and the corresponding amine. The second parallel reaction produces ethane and the corresponding ethyl ester of an α‐amino acid. Calculated thermodynamic and kinetic parameters from PBEPBE calculations were found to be in good agreement with the experimental values. The transition states of the parallel reactions are best described as four‐membered cyclic structures. The intermediate 2‐ethoxy‐ethenamine undergoes a consecutive elimination through a six‐membered cyclic transition state mechanism. Bond indexes and synchronicity (Sy) parameters are in agreement with concerted semi‐polar transition state structures. Copyright © 2008 John Wiley &amp; Sons, Ltd.

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Research paper thumbnail of Theoretical calculations on the mechanism of the elimination kinetics of allyl cyclohexyl-, -amine, -sulfide, -ether, and allyl ethyl ether in the gas phase

Computational and Theoretical Chemistry, 2016

Abstract The mechanism of the gas-phase elimination allyl cyclohexyl amine, allyl cyclohexyl sulf... more Abstract The mechanism of the gas-phase elimination allyl cyclohexyl amine, allyl cyclohexyl sulfide, allyl cyclohexyl ether, and allyl ethyl ether has been studied by using ab initio combined methods CBS-QB3, and Density Functional Theory CAM-B3LYP, MPW1PW91, PBE1PBE, M06, and M062X. Products formation is described below: Theoretical calculations of these reactions support the unimolecular process of these gas-phase eliminations. These thermal decompositions undergo a retro-ene type of mechanism and proceed through a non-planar concerted six-membered cyclic transition structure. The energy of activation follow the order allyl ethyl ether (187.0 kJ/mol) > N-allyl cyclohexyl amine (171.7 kJ/mol) > allyl cyclohexyl ether (170.5 kJ/mol) > allyl cyclohexyl sulfide (137.9 kJ/mol). The polarization of C5–Z6 bond, and the electronegativity of the heteroatom (O, N) increases the reaction rate compared to allyl ethyl ether. Conversely, the S atom is positively charged and its electronic effect causes a high dissymmetry in the TS geometry, which appear to accelerate the decomposition. The rate determining step of these substrates is the change in hybridization from sp3 to sp2 reflected in the bond order in C3–C4. Calculated kinetic and thermodynamic parameters from the M06/6-311++G(d,p) level of theory are in reasonable good agreement with the experimental values.

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Research paper thumbnail of Inquiry of the reaction paths in thermal retro-Diels–Alder reactions in the gas phase: Theoretical study on the concerted and stepwise elimination mechanisms of cyclohexenes

Computational and Theoretical Chemistry, 2015

Abstract The mechanisms of the thermal decomposition of cyclohexene (CH), 4-methylcyclohexene (4M... more Abstract The mechanisms of the thermal decomposition of cyclohexene (CH), 4-methylcyclohexene (4MCH) and 4-vinyl cyclohexene (4VCH) in the gas-phase were studied by means of electronic structure calculations using perturbation MP2 and Density Functional Theory (DFT) methods. Molecular and diradical reaction pathways were calculated. In the case of the 4-susbstituted cyclohexenes two diradical processes were considered. DFT functionals, including a PT2 correction to the correlation energy, gave reasonable results for all reaction paths considered. Calculated parameters obtained with B2PLYP/6-31+G(d,p) are in good agreement with those reported in Tsang’s experimental study. Evaluated kinetic parameters indicate that CH, 4MCH, and 4VCH should follow the concerted molecular reaction pathway. However, it is possible that a fraction of the reactant molecules could overcome the energy barrier for the radical pathway, because of the high temperatures employed in the experimental conditions. The presence of methyl group in 4MCH slightly favors the breaking of C3 C4 bond. The effect of vinyl group is more dramatic, consisted with a resonance effect stabilizing C3 throughout the bond breaking process. NBO charges suggest these processes are discretely polar, since there are slight variations in the electron density along the reaction coordinates. The analysis of the evolution percentages obtained from bond indexes suggests that these reactions are non-synchronous.

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Research paper thumbnail of DFT and ab-initio study on the mechanism of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their isomerization

Journal of Computational Methods in Sciences and Engineering, 2012

The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3... more The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their interconversion have been examined at MP2 and DFT levels of theory. These halide substrates yield isoprene and hydrogen chloride. The results MPW1PW91 calculations agree with the experimental kinetic parameters showing the elimination reaction occurs at greater rate for 1-chloro-3-methylbut-2-ene than that for the 3-chloro-3-methylbut-1-ene isomer. The mechanism for the molecular elimination of 1-chloro-3-methylbut-2-ene suggests proceeding through an uncommon six-membered cyclic transition state for alkyl halides in the gas phase, while 3-chloro-3-methylbut-1-ene eliminates through the usual four-membered cyclic transition state. The elongation and subsequent polarization of the C-Cl bond, in the direction of C^{δ+}…Cl^{δ-}, is rate determining step of these reactions. The isomerization of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene was additionally studied. The 1-chloro-3-methylbut-2-ene converts to 3-chloro-3-methylbut-1-ene easier than the reverse reaction. This means that 1-chloro-3-methylbut-2-ene was found thermodynamically more stable than 3-chloro-3-methylbut-1-ene.

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Research paper thumbnail of The thermal decomposition of 4-bromobutyric acid in the gas phase: A quantum chemical theory calculation

Journal of Computational Methods in Sciences and Engineering, 2012

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Research paper thumbnail of Development of novel serotonin 7‐targeting compounds based on the 2‐dimethylaminotetralin scaffold (1059.13)

The FASEB Journal, 2014

The serotonin (5-HT) 7 G protein-coupled receptor (GPCR) is the most recent 5-HT receptor cloned,... more The serotonin (5-HT) 7 G protein-coupled receptor (GPCR) is the most recent 5-HT receptor cloned, and is expressed in both the periphery and the CNS. Reports propose 5-HT7 receptors are involved in a wide range of CNS functions, including modulation of circadian rhythms, sleep, pain, body temperature, and cognition. 5-HT7 receptors couple to Gαs, leading to activation of adenylyl cyclases and production of cAMP. Due to paucity of available, selective 5-HT7 ligands, the complexity of CNS processes and to a limited number of studies examining 5-HT7, however, there is no consensus about 5-HT7 receptor CNS neuropharmacological function. We have begun an iterative 5-HT7 receptor structure-based ligand synthesis program to develop novel 5-HT7-targeting phenylaminotetralin (PAT) compounds. A molecular model of the 5-HT7 receptor was built by homology to the recently reported structure of the 5-HT1B GPCR, and computational ligand docking studies were undertaken. Computational results were validated by experimenta...

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Research paper thumbnail of Theoretical study on the mechanism of the gas-phase elimination kinetics of alkyl chloroformates

Molecular Physics, 2015

ABSTRACT The theoretical calculations on the mechanism of the homogeneous and unimolecular gas-ph... more ABSTRACT The theoretical calculations on the mechanism of the homogeneous and unimolecular gas-phase elimination kinetics of alkyl chloroformates– ethyl chloroformate (ECF), isopropyl chloroformate (ICF), and sec-butyl chloroformate (SCF) – have been carried out by using CBS-QB3 level of theory and density functional theory (DFT) functionals CAM-B3LYP, M06, MPW1PW91, and PBE1PBE with the basis sets 6-311++G(d,p) and 6-311++G(2d,2p). The chlorofomate compounds with alkyl ester Cβ–H bond undergo thermal decomposition producing the corresponding olefin, HCl and CO2. These homogeneous eliminations are proposed to undergo two different types of mechanisms: a concerted process, or via the formation of an unstable intermediate chloroformic acid (ClCOOH), which rapidly decomposes to HCl and CO2 gas. Since both elimination mechanisms may occur through a six-membered cyclic transition state structure, it is difficult to elucidate experimentally which is the most reasonable reaction mechanism. Theoretical calculations show that the stepwise mechanism with the formation of the unstable intermediate chloroformic acid from ECF, ICF, and SCF is favoured over one-step elimination. Reasonable agreements were found between theoretical and experimental values at the CAM-B3LYP/6-311++G(d,p) level. GRAPHICAL ABSTRACT

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Research paper thumbnail of Effect of structure on reactivity in oxime formation of benzaldehydes

Journal of Physical Organic Chemistry, 1999

... How to Cite. Calzadilla, M., Malpica, A. and Cordova, T. (1999), Effect of structure on react... more ... How to Cite. Calzadilla, M., Malpica, A. and Cordova, T. (1999), Effect of structure on reactivity in oxime formation of benzaldehydes. ... Author Information. Escuela de Quimica, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, 47102, Venezuela. ...

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Research paper thumbnail of Kinetics and mechanism for oxime formation from benzoylformic acid: Electrostatic interactions in the dehydration of carbinolamines

International Journal of Chemical Kinetics, 2008

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Research paper thumbnail of Efecto de la naringenina, hesperetina y sus formas glicosidadas sobre la replicación de la cepa 17D del virus de la fiebre amarilla

Infections produced by flaviviruses are threats to public health worldwide. The absence of effect... more Infections produced by flaviviruses are threats to public health worldwide. The absence of effective drugs treatment makes imperative the quest for efficient antivirals. Using a plaque inhibition assay we studied the antiviral action of the non-cytotoxic flavanones naringenin, hesperetin, and their glycoside forms on the replication of the 17D strain of yellow fever virus (YFV17D). Using plaque assay the glycosylated forms did not show antiviral effect at the highest concentration used, naringenin and hesperetin reduced the plaque size and the infectious titer up to 85.51% and 100% respectively at the maximum concentration employed. The effective dose (ED 50 ) of naringenin (0.0013 uM), calculated by plaque assay, was approximately tenfold lower than hesperetin (ED 50 0.01 uM), and neither showed any virucidal effect. Evaluation of kinetic entrance of YFV to cell showed that after 2h of infection 80% of the virus was already into the cell, but in the presence of naringenin or hesper...

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