The utility of the PM3 method for predicting the reactivities of cyanoethenes in diels-alder reactions with pyrrole

The reliability of PM3 for predicting the reactivity of cyanoethenes in Diels-Alder reactions with pyrrole was tested. Using frontier orbital theory it was predicted that the reaction is LUMO dienophile controlled, and the reaction should be facilitated in comparison to cyclopentadiene additions (pyrrole has higher HOMO energy). The transition structures were generated and compared with similar ones generated with both ab initio and PM3 calculations for cyclopentadiene additions: The geometries of the transition structures are similar, although the new CC forming bonds are 2–6% shorter, and the degree of asynchronicity is higher. The prediction of the activation barriers with the PM3 method failed totally. The preferred exo isomer in each case, indicated that the predicted stereoselectivity was incorrect. The prediction of the relative reactivity was also unreliable. Qualitative analyses of similar series of compounds can be obtained by frontier orbital energy correlations. All conclusions were made on the assumption that the reaction is concerted, which does not exclude the possibility that PM3 might be able to predict reliable reaction barriers if some other mechanisms are considered.     

Koopmans-like approximation in the Kohn-Sham method and the impact of the frozen core approximation on the computation of the reactivity parameters of the density functional theory

A Koopmans-like approximation is introduced in the spin-polarized version of the Kohn-Sham (KS) density functional theory to obtain a relation between KS orbital energies and vertical ionization potential and electron affinity. Expressions for reactivity indexes (like electronegativity, hardness, electrophilicity, and excitation energies) include KS frontier orbital energies and additional contributions associated with the self-interaction correction. Those reactivity parameters were computed with different exchange-correlation functionals to test the approach for a set of small molecules. The results show that the present approximation provides a better way to estimate hardness, electronegativity, and electrophilicity than just the use of frontier orbital energy values. However KS HOMO and LUMO energy gap gives a better agreement with excitation energies.     

Computational investigation of the suitability of heterocyclic aromatic compounds with two heteroatoms in the 1 and 3 ring positions as dienes for the diels alder reaction

Semiempirical and density functional theory computational studies were carried out with the target determining the reactivity of five membered heterocycles with heteroatoms in the 1 and 3 positions as dienes for Diels-Alder reactions. The relative reactivity was evaluated in their reaction with acetylene, ethylene, and cyclopropene as dienophiles for cycloaddition. Qualitative criteria such as uniformity of heterocycle bond orders, change of bond orders and frontier molecular orbital energies in transformation of reactants into transition state structures were used to determine the relative reactivity in comparison with furan. These results are compared with the computed activation barriers as well as with experimental findings, where available. If cycloaddition is feasible with these heterocycles, a new synthetic transformation of simple organic compounds to valuable prostaglandin derivatives can be accomplished.     

Density functional theory study on the effect of substitution and ring annelation to the rim of corannulene

B3LYP/6-311G calculations indicate that annelation of a five-membered ring to the rim of corannulene and substitution to all the rim carbons lowers the barrier for bowl-to-bowl inversion. Singlet-triplet energy differences, frontier orbital analysis, and nucleus-independent chemical shift (NICS) values indicate significant enhancement of the reactivity when the substitutions involve exocyclic double bonds. Bowl-to-bowl inversion barrier, curvature, and reactivity for unsaturated and saturated five-membered ring-annelated corannulenes are analogous to decamethyl- and decamethylene-substituted corannulenes.     

A NEW REACTIVITY INDEX——PSEUDO ORBITAL INDEX

The concept of pseudo orbital has been proposed, which includes the interactions of all the orbitals and extends the applicable limit of Fukui's frontier orbitals. An example shows that the pseudo orbital reactivity indexes are probably able to explain more complicated phenomena in chemical reactions.     

Theoretical study of the interaction of molecular oxygen with copper clusters

A new method based on frontier orbital theory has been used to investigate the binding site of molecular oxygen to neutral and anion copper clusters. It has been shown that one can make useful predictions of the binding sites based on the knowledge of the donor local reactivity of the cluster using the condensed Fukui function, f(-)(Ff). In this way, it was found that Cu(3), Cu(5), and Cu(5)(-) have the highest reactivity toward molecular oxygen.     

一种新的反应性指数：赝轨道活性指数

Fukui提出的前线轨道理论在预测反应活性方面获得了极大的成功。在某些情况下,除了前线轨道之外,还必须考虑其它轨道之间的相互作用。本文提出赝轨道的概念,将所有内层轨道的作用包括在赝轨道参数之内。扩展了前线轨道理论的适用范围。并用硝基苯和苯睛的硝化反应的定位效应为例说明了赝轨道指数的应用。     

Theoretical study of the corrosion inhibition of some bipyrazolic derivatives: a conceptual DFT investigation

Corrosion inhibition of copper through six bipyrazolic compounds has been elucidated by means of density functional theory (DFT)-derived reactivity indexes. The DFT calculated parameters and experimental corrosion inhibition efficiency (IE%) indicate that their inhibition effect is closely related to the frontier orbital energies, polarizability, electronic chemical potential and global nucleophilicity. The quantum chemistry calculations were performed at the B3LYP/6-31G (d) level. The theoretical results, predicted using DFT-based reactivity indexes, are in good agreement with experimental outcomes.     

The structure and possible catalytic sites of Mo(3)S(9) as a model of amorphous molybdenum trisulfide: a computational study

The structure and reactivity of Mo(3)S(9) clusters, taken as a model for amorphous molybdenum trisulfide, have been investigated at the B3LYP density functional level of theory. Two computed ground-state cluster structures are close in energy and have similar structural parameters and vibrational modes. These values agree well with the available experimental data. These cluster structures are considered to be formed simultaneously during the preparation process of catalysts. Their catalytic activity has been analyzed on the basis of frontier molecular orbital properties (FMO). It is mainly due to 4d-type orbitals of the unsaturated molybdenum centers without terminal sulfur coordination. The small HOMO-LUMO gaps suggest that Mo(3)S(9) clusters can act as Lewis acids or Lewis bases.     

Theoretical study of the Diels-Alder reactions between singlet (1Delta g) oxygen and acenes

The G3(MP2) method has been employed to study the 1,4-addition reactions between singlet oxygen and five acenes, including benzene, naphthalene, anthrecene, tetracene, and pentacene. In all, nine pathways between O(2) and the five acenes have been investigated. Our calculated results indicate that all nine pathways are concerted and exothermic and that the most reactive sites on the acenes are the center ring's meso-carbons. In addition, reactivity increases along the series benzene < naphthalene < anthrecene < tetracene < pentacene. This trend is identical to that of aromaticity for the five acenes. A correlation between reactivity and aromaticity is briefly rationalized with natural bond orbital (NBO) analysis and frontier molecular orbital (FMO) analysis. Furthermore, some experimental kinetics data from the literature supporting the calculated results are cited.     

Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH3) and boron trifluoride (BF3) as a function of angles of reorganization from planar (D3h) to pyramidal (C3v) shape

In chemical response the BH₃ and BF₃ molecules undergo the physical process of planar (D_3h) to pyramidal (C_3v) reorganization in shape as the condition precedent to the event of chemical reaction under the requirement of symmetry. A frontier orbital and density functional study of the variation of the stability of electronic structures and chemical reactivity of associated with the physical process of D_3h to C_3v geometry reorganization has been performed. The theoretical parameters viz. eigenvalues of HOMO and LUMO, the HOMO and LUMO energy gap, the global hardness and global softness, the chemical potential, the condensed Fukui function, and local softness of B atom, the reaction site, have been computed over a wide range of ∠XBX angles. The nature of variation in the intrinsic chemical reactivity, global and local, of the molecules associated with their geometry reorganization during the chemical event of charge transfer interaction involving their frontier molecular orbitals has been quantitatively explored. The hardness profiles as a function of reaction coordinates are consistent with the principle of maximum hardness (PMH). Results demonstrate that the hardness and softness are not a static and invariable property of molecules but a dynamic and variable function of molecular structure. The hardness parameters and the HOMO–LUMO gap of the molecules are so modified with the distortion of molecular geometry that, after a certain stage of molecular deformation, the profiles of such parameters of the molecules intersect and cross each other, signifying that the relative order of the intrinsic hardness of their equilibrium geometry is reversed. The intrinsically hard molecule BF₃ becomes softer than the intrinsically soft molecule BH₃ as a consequence of structural distortion. The increase in chemical reactivity computed in terms of density functional parameters are transparent and justified in terms of the profiles of the eigenvalues of the frontier orbitals. The profiles of chemical potential reveal the inherent difference in the tendency of backdonation from two molecules. The computed values of Fukui functions and local softness parameters of the B atom site demonstrate that the concept of local softness can be exploited for a theoretical analysis and understanding of the characteristic chemical events of the molecules under consideration. The profiles of the Fukui functions and local softness parameters of the two molecules seem to reflect and reveal their intrinsic difference in the tendency of receiving donation in the LUMO (electrophilicity) and that of backdonation from the HOMO (nucleophilicity) and the inherent difference of overall reactivity of the two molecules by a simultaneous operation of two opposing processes of charge transfer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Reactivite des acylaldocetenes dans la cycloaddition intramoleculaire

The reactivity of acylaldoketenes, short-lived species generated by flash thermolysis of ?-ethylenic β-ketoesters, in [2 + 2] intramolecular cycloaddition reactions, has been examined. The observed regiospecificity can be rationalized by frontier orbital theory.     

A theoretical study of the addition of silyl radicals to olefinic monomers

In this paper, the high reactivity of silyl macroradicals toward double bonds of olefinic compounds has been explained by means of quantum‐mechanical calculations through their frontier orbital characteristics. In this way, the main orbital interaction corresponds to the overlapping between the SOMO of the disilyl radical and the LUMO of the olefin. In order to obtain more accurate results of differential reactivity, an orbitalic SOMO‐HOMO interaction should be included in addition to the main SOMO‐LUMO one. Also, we theoretically studied the regioselectivity of the addition of silyl radicals to double bonds obtaining similar results as for carbon centered radicals where the reaction takes place on the less hindered carbon of the olefin. Regarding to the geometrical and electronic parameters, it has been shown that carbon radicals have a sp² geometry and a negative charge on the radical center whilst silyl radicals have a sp³ goemetry and a positive charge. Both factors contribute to the enhanced reactivity of silyl radicals with respect to carbon ones.     

Structural,Electronic, Reactivity,and Conformational Features of 2,5,5-Trimethyl-1,3,2-diheterophosphinane-2-sulfide,and Its Derivatives: DFT,MEP, and NBO Calculations

In this study, we used density functional theory (DFT) and natural bond orbital (NBO) analysis to determine the structural, electronic, reactivity, and conformational features of 2,5,5-trimethyl-1,3,2-di-heteroatom (X) phosphinane-2-sulfide derivatives (X = O (compound 1), S (compound 2), and Se (compound 3)). We discovered that the features improve dramatically at 6-31G** and B3LYP/6-311+G** levels. The level of theory for the molecular structure was optimized first, followed by the frontier molecular orbital theory development to assess molecular stability and reactivity. Molecular orbital calculations, such as the HOMO–LUMO energy gap and the mapping of molecular electrostatic potential surfaces (MEP), were performed similarly to DFT calculations. In addition, the electrostatic potential of the molecule was used to map the electron density on a surface. In addition to revealing molecules’ size and shape distribution, this study also shows the sites on the surface where molecules are most chemically reactive.     

烷基对羰基反应性能影响的CNDO／2研究

对于碳-氧双键和亲核试剂的加成反应,由于负离子进攻为反应速度决定步骤,人们普遍认为羰基的反应性能主要取决于碳原子上的正电荷量,正电荷愈多亲核试剂愈易加成,全部反应也愈易进行。并认为酮的羰基的亲电能力比醛弱,这是由于酮的羰基和2个烃基相结合,如为烷基,具有给电子作用,则增加羰基碳原子电负性,降低其亲电能力。     

Reactivity of pyrrole pigments. Part 10 MINDO/3 calculations on bile pigments

The applicability of the MINDO/3 method is evaluated for tetrapyrrolic bile pigments: geometries from already calculated dipyrrolic partial models have been used to reduce the calculation time. Net atomic charges and reactivity parameters obtained from the frontier orbital model, i.e. HOMO and LUMO distribution on the molecule, are reported for several conformations.

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Reaktivität von Pyrrolpigmenten, 10. Mitt. MINDO/3-Rechnungen von Gallenpigmenten

Zusammenfassung Es wird der Einsatz von MINDO/3 für tetrapyrrolische Gallenpigmente beschrieben. Um die Rechenzeit herabzusetzen, wurden geometrische Daten verwendet, die vorher für dipyrrolische Partialstrukturen ermittelt worden waren. Für mehrere Konformationen werden Ladungsdichten und Reaktivitätsparameter nach dem Frontier-Orbital-Modell, nämlich HOMO- und LUMO-Verteilung, berichtet.

     

The Analysis of Os≡C Bond and Electric Field Influence on the Properties in the Osmium Carbyne Complex OsCl3 (≡CCH2CMe3 )(PH3 )2: A Theoretical Insight

In this paper, we study the effect of electric field on the dipole moment, electronic structure, and frontier orbital energy in the osmium carbyne complex OsCl₃ (≡CCH₂CMe₃ )(PH₃ )₂ using MPW1PW91 quantum chemical computations. We demonstrate the nature of the chemical bond between the [OsCl₃ (PH₃ )₂]⁻ and [CCH₂CMe₃ ]⁺ fragments through energy and charge decomposition analyses. We also estimate the percentage composition in terms of the specified groups of frontier orbitals for this complex to investigate the feature in the metal–ligand bonds. Quantum theory of atoms in molecules (QTAIM ) is applied to elucidate the Os≡C bond in the complex. Also, the influence of external electric field on the energy, frontier orbital energies, and HOMO–LUMO gap values is analyzed.