Salim M. Khalil

MINDO-Forces calculation of molecular geometries and reaction paths

A new method for the minimization of molecular energies is described, based on the Murtagh-Sargent procedure and the MINDO/2(3) semiempirical MO method. The derivative of energy is calculated according to the Pulays Force method. This method was applied to the calculation of heats of formation and geometries of different organic molecules. The results agree well with the experimental and theoretical values known in the literature. The MINDO-Forces method was applied to the calculation of the internal rotation barrier of the benzyl carbonium ion. The calculated value 18.79 kcal/mol agrees well with the theoretical values known in the literature. The MINDO-Forces method was applied to the calculation of the internal rotation barrier of cyclopropyl carbinyl cation. The calculated rotation barrier, 21.28 kcal/mol is in agreement with the known theoretical values and with the expectation based on the NMR measurement of the barrier height in cyclopropyl dimethyl-carbinyl cation.

A Theoretical Study of Carbohydrates as Corrosion Inhibitors of Iron

The inhibitive effect of fructose, glucose, lactose, maltose, and sucrose against the iron corrosion is investigated using density functional theory at the B3LYP/6-31 G level (d) to search the relation between the molecular structure and corrosion inhibition. The electronic properties such as the energy of the highest occupied molecular orbital (HOMO), the energy of lowest unoccupied orbital (LUMO), the energy gap (LUMO-HOMO), quantum chemical parameters such as hardness, softness, the fraction of the electron transferred, and the electrophilicity index are reported. The inhibition efficiency of the investigated carbohydrates follows the trend: maltose

A DFT Study on the Stepwise Fluorinated Methylenecyclopropane ⇋ 1-Methylcyclopropene System

Density functional theory (DFT) calculations have been performed to calculate the optimized geometries of stepwise fluorinated methylenecyclopropanes and 1-methylcyclopropenes. Increasing the number of fluorine atoms caused a destabilization of methylenecycopropane. Perfluorinated 1-methylcyclopropene was found to be present in substantial concentration. This is supported by calculations of the Gibbs free energy, isodesmic reactions and orbital energies (HOMO-LUMO). These results are compared with the fluorinated cyclopropanes keto-enol system. Enthalpies, entropies and dipole moments are reported.

A Theoretical Study of Monosubstituted Cyclopropenyl System

Abstract MONDO-Forces calculations have been performed, with complete optimization of geometry on X-cyclopropenyl system (cations, radicals and anions), where X is H, O-, OH, CH3 , CN, NO2 , F and CF3 . All substituents prefer planar structure when substituted on both cations and radicals, while they prefer pyramidal structure in the case of anions except CF3 . The substituents O-, OH and F act as electron releasing, while CHO, NO2 and CF3 act as electron withdrawing when substituted on cyclopropenyl system. CH3 and CN show amphielectronic behaviour. They act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand. In the case of cations and radicals, all substituents were found to increase the vicinal bonds and decrease the distal bonds and bond angles to which the substituent is attached. For anions the substitutents show no such regularity because the substituents are out of the three-membered ring plane. All substituents increase the stability of the cyclopropenyl system except CF3 in the case of the cation.

A Theoretical Study of Substituted Cyclobutanones and Their Enols

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

A Theoretical Study of Substituted Stepwise Fluorinated Cyclopropanone Keto-Enol System

MINDO-Forces calculations have been performed with complete optimization of the geometries on stepwise fluorinated cyclopropanones and their enols. Increase in the number of fluorine atoms causes destabilization of cyclopropanone. Perfluorinated enol was found to be present in substantial concentration, as was mentioned in previous work. This is supported by calculations of Gibbs free energies and isodesmic reactions. Geometrical parameters, heats of formation, electron densities, dipole moments and orbital energies (HOMO-LUMO) are reported.

MINDO-Forces Study of α-Substituted Cyclopropyl and Isopropyl Radicals

Abstract The structures of α-X-cyclopropyl and α-X-isopropyl radicals (X = H, O-, OH, NH2, CH3, NO2, CHO, CN, F and CF3) are reported using MINDO-Forces MO method. In both radicals the planar structure is prefered over the pyramidal. All the substituents are stabilizing; the O- group is the most stabilizing substituent, while F group has little effect. O- , OH, F substituents are electron releasing groups on cyclopropyl ring, while NO2, CHO and CF3 are electron widthdrawing. For isopropanes and x-X-isopropyl radicals, O-, OH, NH2 and F act as electron releasing, while NO, and CF3 act as electron withdrawing. The strain energies of the cyclopropyl radicals (43.8-23.7 kcal/mol) are compared with those of similarly substituted cyclopropanes. Dipole moments and spin densities are reported.

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.

MINDO-Forces Study on the Relative Stabilities of Hydroxy- and Aminopyridine Tautomers

Relative stabilities of monosubstituted hydroxy- and aminopyridine tautomers have been calculated using the semiempirical MINDO-Forces MO method with full geometries optimization. The lactim tautomers proved to be more stable except in the case of 2-hydroxypyridine. The results are in good agreement with some theoretical and experimental values.

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.