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

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

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 Calculation of Some Substituted Phenylallyl Cations

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.

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

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.

A Theoretical Study of Substituted Cyclopentanones and their Enols

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

EXACT MANY-BODY APPROACH TO MAGNETISM AND CLUSTER STRUCTURE

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.

Ab initio MO study of protonation of carbamic acid, methyl carbamate and methyl N-methylcarbamate

The ab initio SCF method was applied to the protonation of the carbonyl group in carbamic acid and its methyl derivatives, viz. methyl carbamate and methyl N-methylcarbamate. Complete geometry optimization was accomplished for these compounds and their protonated species using the MINI-1, 3-21 G, and 6-31 G* bases and the proton affinities were calculated at the MINI-1, 3-21 G, 6-31 G*, and 6-31 G** levels. 2nd and 3rd order Moller-Plesset perturbation calculations were also performed for examining the effect of the correlation energy on the calculated protonation energies. The carbonyl protonation energies were found to increase in order carbamic acid < methyl carbamate < methyl N-methylcarbamate. The absolute values of calculated gas phase proton affinities depend on the basis used and way of evaluating the correlation energy. The results are discussed with respect to the theoretical proton affinities of structurally related amides and to related available theoretical gas phase proton affinities.

A Theoretical Study of 2-Substituted Allyl Cations and Anions

MINDO-Forces calculations are reported, after complete geometry optimization, for 2-X-allyl cations and anions, where X is O- , OH, NH2, CH3, NO2, CN, CF3, F, CHO.In the case of the allyl cation, it was found that the substituents O- , OH, NH2 are stabilizing, CH3 is slightly stabilizing and all other substituents are destabilizing.In the case of the allyl anions, all the substituents are stabilizing. It was found that the substituents CH3, O- , CN show the amphielectronic behaviour. Calculations predict no (1,3) π interaction in 2-substituted ally cations and anions.

Ion solvation by dipolar aprotic solvents. An ab initio study

The paper deals with the solvation of Li+, Be2+, Na+, Mg2+, and Al3+ ions in dimethyl sulphoxide, dimethylformamide, acetonitrile, and water. The ab initio quantum chemical method was used to calculate the solvation energies, molecular structures, and charge distributions for the complexes water···ion, acetonitrile···ion, dimethyl sulphoxide···ion, and dimethylformamide···ion. The interaction energies were corrected for the superposition error. Complete geometry optimization was performed for the complex water···ion. Some generalizations are made on the basis of the results obtained.