Mindo-Forces Study on the Keto-Enol Tautomerism of α-Substituted Acetaldehydes XCH2CH=O (X = H, F, Oh, Cn, NH2, NO2, CH3, CF3, OCH3): Comparison with Acetyl Derivatives

2004 ◽  
Vol 59 (12) ◽  
pp. 980-986
Author(s):  
Wasim F. Al-Halasah ◽  
Salim M. Khalil
Keyword(s):  
Theoretical Calculations ◽  
Geometry Optimization ◽  
Substituent Effects ◽  
Geometrical Parameters ◽  
Free Energies ◽  
Electron Densities ◽  
The Stability ◽  
Complete Geometry Optimization

MINDO-Forces calculations with complete geometry optimization have been performed on α- substituted acetaldehydes XCH2CH=O and their enols (X = H, F, OH, CN, NH2, NO2, CH3, CF3, OCH3). All substituents were found to decrease the stability of the acetaldehyde and mostly in the case of electron withdrawing capacity (e. g NO2 and CF3). This agrees with theoretical calculations, except in the case of F. The substituent effects on the stabilities in this study are compared with results obtained from our previous theoretical calculations on acetyl derivatives. Geometrical parameters, electron densities, and Gibbs free energies are reported.

MINDO-Forces Study on Substituted Nitromethane ⇋ aci-Nitromethane Tautomerism

2005 ◽  
Vol 60 (1-2) ◽  
pp. 47-53
Author(s):  
Bareehan M. Salim ◽  
Salim M. Khalil
Keyword(s):  
Theoretical Calculations ◽  
Geometry Optimization ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Free Energies ◽  
Electron Densities ◽  
Isodesmic Reactions ◽  
Complete Geometry Optimization

MINDO-Forces calculations with complete geometry optimization have been performed on nitromethane, aci-nitromethane and X-substituted nitromethane and aci-nitromethane (X = F, OH, NH2, CH3, CN, CF3, NO2, CHO). It is found that nitromethane is more stable than aci-nitromethane by 9.337 kcal/mol. This agrees with theoretical calculations. Thermodynamically, substituted aci-nitro tautomers are more stable than the corresponding nitromethane, except in case of the substituent F. Geometrical parameters, heats of formation, electron densities, Gibbs free energies and isodesmic reactions are reported.

MINDO-Forces Study on the Substituent Effect in the Keto-Enol Tautomerism of Acetyl Derivatives

2004 ◽  
Vol 59 (4-5) ◽  
pp. 299-308
Author(s):  
Wasim F. Al-Halasah ◽  
Ali Mahasnah ◽  
Salim M. Khalil
Keyword(s):  
Vinyl Alcohol ◽  
Substituent Effect ◽  
Theoretical Calculations ◽  
Geometry Optimization ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Free Energies ◽  
Orbital Energies ◽  
Homo Lumo ◽  
Complete Geometry Optimization

MINDO-Forces calculations with complete geometry optimization have been performed on acetaldehyde, vinyl alcohol and acetyl derivatives CH3COX(X=H, F, OH, CN, NH2, NO2 , CH3 , CF3,OCH3). It was found that acetaldehyde is more stable than vinyl alcohol by 10.451 kcal/mol. Thermodynamically, keto tautomers are more stable than their enol counterparts. This agrees with theoretical calculations. The electron releasing substituents tend to stabilize keto tautomers, while the electron withdrawing substituents tend to destabilize the keto tautomers, relative to the parent. Geometrical parameters, heats of formation, electron densities, Gibbs free energies and orbital energies (HOMO-LUMO) are reported.

MINDO – Forces Calculation of Some Substituted Phenylallyl Cations

2004 ◽  
Vol 59 (12) ◽  
pp. 971-976
Author(s):  
Salim Y. Hanna ◽  
Salim M. Khalil ◽  
Moafaq Y. Shandala
Keyword(s):  
Correlation Analysis ◽  
Electron Density ◽  
Molecular Orbital ◽  
Geometry Optimization ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Molecular Orbital Calculations ◽  
Electron Densities ◽  
Stabilization Energies ◽  
Complete Geometry Optimization

MINDO-Forces SCF-molecular orbital calculations with complete geometry optimization have been performed on x-substituted phenylallyl cations, where x is H, OCH3, NH2, NO2, CN, F and CH3, in ortho, meta, or para positions. Optimized geometrical parameters, electron densities, heats of formation and stabilization energies were obtained. The substitutent effect on the geometrical parameters and the electron density are discussed by correlation analysis.

scholarly journals A Theoretical Study of Substituted Cyclopentanones and their Enols

2003 ◽  
Vol 58 (12) ◽  
pp. 738-748 ◽  
Author(s):  
Meisa S. Al-Noeemat ◽  
Reem A. Al-Ma’ani ◽  
Salim M. Khalil
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Theoretical Study ◽  
Geometry Optimization ◽  
Density Functional Theory Calculations ◽  
Geometrical Parameters ◽  
Free Energies ◽  
Strong Electron ◽  
Functional Theory ◽  
Complete Geometry Optimization

MINDO-Forces calculations with complete geometry optimization have been performed on cyclopentanone and its enol counter part, perfluorination of cyclop entanone and its enol counterpart and X-cyclopentanones and their X-enols, where X is NO2, CF3, CN, OH, NH2 and O−. It was found that ketone is more stable than its enol counterpart. Perfluorination destabilizes ketone on the expense of enol. These results agree with the experimental results and density functional theory calculations. All substituents are destabilizing except O− in the case of cyclopentanone. It was found that NO2 and CF3 behave as strong electron withdrawing groups, CN and NC show amphielectronic behavior, and the substituents OH,NH2 and O− behave as electron releasing groups with O− being strongest. Geometrical parameters, heats of formation, entropies, and Gibbs free energies are reported

Substitutent Effects on the Geometrical Properties of 1-Phenylallyl Alcohol

2005 ◽  
Vol 60 (4) ◽  
pp. 265-270
Author(s):  
Salim Y. Hanna ◽  
Salim M. Khalil ◽  
Moafaq Y. Shandala
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Substituent Effects ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Molecular Orbital Calculations ◽  
Electron Densities ◽  
Geometrical Properties ◽  
Stabilization Energies

Abstract Optimized geometrical parameters, electron densities, heats of formation and stabilization energies have been obtained on X-substituted phenylallyl alcohols, where X is H, OCH3, NH2, CN, F and CH3 at ortho, meta, and para positions, using MINDO-Forces SCF-molecular orbital calculations. The substituent effects on the geometrical parameters and the electron density are discussed.

scholarly journals Tracing The Acid-Base Catalytic Properties Of MON2O Mixed Oxides (M=Be, Mg, Ca; N=Li, Na, K) By Theoretical Calculations

2021 ◽  
Author(s):  
Dawid Faron ◽  
Piotr Skurski ◽  
Iwona Anusiewicz
Keyword(s):  
Alkali Metal ◽  
Gas Phase ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Theoretical Calculations ◽  
Lewis Acidity ◽  
Free Energies ◽  
Acid Base ◽  
The Stability ◽  
Fragmentation Processes

Abstract The stability and acid-base properties of MON2O mixed oxides (where M = Be, Mg, Ca; N = Li, Na, K) are studied by using ab initio methods. It is demonstrated that (i) the basicity of such designed systems evaluated by estimation of electronic proton affinity and gas-phase basicity (defined as the electronic and Gibbs free energies of deprotonation processes for [MON2O]H+) were found significant (in the ranges of 272–333 kcal/mol and 260–322 kcal/mol, respectively); (ii) in each series of MOLi2O/MONa2O/MOK2O the basicity increases with an increase of the atomic number of alkali metal involved; (ii) the Lewis-acidity of the corresponding [MON2O]H+ determined with respect to hydride anion (assessed as the electronic and Gibbs free energies of H− detachment processes for [MON2O]H2) decreases as the basicity of the corresponding oxide increases. The thermodynamic stability of all [MON2O]H2 systems is confirmed by estimating the Gibbs free energies for the fragmentation processes yielding either H2 or H2O.

scholarly journals Tracing the acid-base catalytic properties of MON2O mixed oxides (M = Be, Mg, Ca; N = Li, Na, K) by theoretical calculations

2021 ◽  
Vol 27 (7) ◽  
Author(s):  
Dawid Faron ◽  
Piotr Skurski ◽  
Iwona Anusiewicz
Keyword(s):  
Gas Phase ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Theoretical Calculations ◽  
Lewis Acidity ◽  
Ab Initio Methods ◽  
Free Energies ◽  
Acid Base ◽  
The Stability ◽  
Fragmentation Processes

AbstractThe stability and acid-base properties of MON2O mixed oxides (where M = Be, Mg, Ca; N = Li, Na, K) are studied by using ab initio methods. It is demonstrated that (i) the basicity of such designed systems evaluated by estimation of electronic proton affinity and gas-phase basicity (defined as the electronic and Gibbs free energies of deprotonation processes for [MON2O]H+) were found significant (in the ranges of 272–333 and 260–322 kcal/mol, respectively); (ii) in each series of MOLi2O/MONa2O/MOK2O, the basicity increases with an increase of the atomic number of alkali metal involved; (ii) the Lewis acidity of the corresponding [MON2O]H+ determined with respect to hydride anion (assessed as the electronic and Gibbs free energies of H− detachment processes for [MON2O]H2) decreases as the basicity of the corresponding oxide increases. The thermodynamic stability of all [MON2O]H2 systems is confirmed by estimating the Gibbs free energies for the fragmentation processes yielding either H2 or H2O.

A THEORETICAL STUDY OF THE SUBSTITUENT EFFECT ON THE STABILITY OF COLLAGEN

2004 ◽  
Vol 03 (02) ◽  
pp. 225-243 ◽  
Author(s):  
JUN-MIN QUAN ◽  
YUN-DONG Wu
Keyword(s):  
Electrostatic Interactions ◽  
Triple Helix ◽  
Density Functional ◽  
Theoretical Calculations ◽  
Substituent Effects ◽  
Binding Energies ◽  
Model Studies ◽  
Collagen Triple Helix ◽  
Triple Helices ◽  
The Stability

Theoretical calculations have been carried out to investigate the effect of the 4(R)-substituents ( OH , F , NH 2, and [Formula: see text]) in proline on the stability of the collagen triple helix. A series of substituted proline models were studied first with density functional (B3LYP/6-31+G*) calculations. The solvent effect was studied using the SCIPCM method. While the F , OH and NH 2 groups increase the stability of the trans-up conformation with respect to the trans-down conformation, [Formula: see text] appears to favor the trans-down conformation in an aqueous solution. Second, the triple helices of the tripeptide models, Ac – Pro – Pro(X) – Gly – H with the two proline residues in the down/down and down/up puckering conformations, were optimized with a repeating unit approach using the HF/6-31G* method. For the Ac – Pro – Pro – Gly – H model peptide, the calculated binding energies of the two triple helices with the different puckering modes are similar. All four substituents, F , OH , NH 2, and [Formula: see text], considerably increased the binding energy of the down/up helix, but only [Formula: see text] stabilizes the down/down triple helix. Our calculations indicate that the inter-chain electrostatic interactions involving the 4(R)-substituents play an important role in stabilizing triple helical collagen models and allow the rationalization of all available experimental observations. Further model studies indicate that the substituent effects by the F , OH and NH 2 substituents are local while the effect of [Formula: see text] is long-range in nature.

EXACT MANY-BODY APPROACH TO MAGNETISM AND CLUSTER STRUCTURE

1996 ◽  
Vol 03 (01) ◽  
pp. 447-451
Author(s):  
G.M. PASTOR ◽  
R. HIRSCH ◽  
B. MÜHLSCHLEGEL
Keyword(s):  
Structural Changes ◽  
Electronic Excitation ◽  
Cluster Structure ◽  
Geometry Optimization ◽  
Electron Correlations ◽  
Many Body ◽  
The Stability ◽  
Small Clusters ◽  
Cluster Ferromagnetism ◽  
Complete Geometry Optimization

The magnetic and structural properties of small clusters having N≤8 atoms were determined rigorously in the framework of the Hubbard model by performing the exact many-body electronic calculations together with a complete geometry optimization. We discuss the resulting interplay between electron correlations, magnetism, and cluster structure at T=0, as well as the stability of cluster ferromagnetism against temperature-induced electronic excitation and structural changes.

scholarly journals A Theoretical Study of Substituted Cyclobutanones and Their Enols

2004 ◽  
Vol 59 (11) ◽  
pp. 838-844
Author(s):  
Mohammad I. Sway ◽  
Iyad D. Al-Shawabkeh ◽  
Salim M. Khalil
Keyword(s):  
Free Energy ◽  
Gibbs Free Energy ◽  
Theoretical Study ◽  
Theoretical Calculations ◽  
Heats Of Formation ◽  
Geometrical Parameters ◽  
Electron Densities ◽  
Complete Optimization ◽  
Electron Withdrawing Substituents

MINDO-Forces calculations have been performed with complete optimization of the geometry on cyclobutanone and its enol counterpart, perfluorination of cyclobutanones and enol counterparts, and X-cycolobutanones and their X-enols, where X is NO2, CF3, CN, OH, NH2 and F. It was found that ketone is more stable than its enol counterpart. Perfluorination destabilizes ketone on the expense of enol. These results agree with experimental and theoretical calculations. Electron releasing substituents (NH2, OH, F) stabilize cyclobutanone, while electron withdrawing substituents (CF3, NO2) destabilize it. CN substituents have almost no effect on the stabilization of this keto-enol system. Geometrical parameters, heats of formation, electron densities and Gibbs free energy are reported

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