Search results for "Electron localization function"
showing 10 items of 55 documents
Understanding the regioselectivity in hetero Diels–Alder reactions. An ELF analysis of the reaction between nitrosoethylene and 1-vinylpyrrolidine
2013
[EN] The regioselectivity in the hetero Diels-Alder reaction between nitrosoethylene 1 and 1-vinylpyrrolidine 2 has been studied by a comparative ELF bonding analysis along the IRC of the endo/ortho and endo/meta regioisomeric channels at the B3LYP/6-31G*. level. Along the most favorable endo/ortho regioisomeric channel, the C-C sigma bond is first formed by coupling of two pseudoradical centers located at the most electrophilic carbon of 1 and the most nucleophilic center of 2. Formation of these relevant pseudoradical centers, which depend on the total charge transfer process along the polar reaction, and not on the approach mode of each reagent, is well characterized by analysis of the a…
Energetics of hydride and electron pair attachment to EX30/+ (E=B, C, Al, Si and X=F, Cl, Br, I) and the study of bonding trends among EX30/+, EX32−/…
2004
Abstract A theoretical gas-phase “ligand-free” or “electron pair affinity” (EPA) approach, based on CCSD(T)/(SDB-)cc-pVTZ//MP2/(SDB-)cc-pVTZ electronic structure calculations, is introduced as a possible means for determining Lewis acidity trends among planar EX30/+ (E = B, C, Al, Si; X = F, Cl, Br, I) species. In this treatment, the free electron pair is considered to be an extreme Lewis base. The calculated EPA values are compared with experimental Lewis acidities, previously calculated fluoride ion affinity (FIA) and hydride ion affinity (HA) trends, and are found to exhibit reasonable correlations in all cases. The bonding in the planar and trigonal pyramidal conformations of EX30/+ and…
Nature of the ring-closure process along the rearrangement of octa-1,3,5,7-tetraene to cycloocta-1,3,5-triene from the perspective of the electron lo…
2011
We analyze the behavior of the energy profile of the ring-closure process for the transformation of (3Z,5Z)-octa-1,3,5,7-tetraene 5 to (1Z,3Z,5Z)-cycloocta-1,3,5-triene 6 through a combination of electron localization function (ELF) and catastrophe theory (CT). From this analysis, concepts such as bond breaking/forming processes, formation/annihilation of lone pairs, and other electron pair rearrangements arise naturally through the reaction progress simply in terms of the different ways of pairing up the electrons. A relationship between the topology and the nature of the bond breaking/forming processes along this rearrangement is reported. The different domains of structural stability of …
Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory
2021
The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the sum of those of butadiene and ethaniminium. The superelectrophilic character of dieniminiums accounts for the high intramolecular global electron density transfer taking place from the diene framework to the iminium one at the transition state structures (TSs) of these IIDA reactions, which are classified as the forward electro density flux. The activation enthalpy ass…
Carrier confinement in Ge/Si quantum dots grown with an intermediate ultrathin oxide layer
2012
We present computational results for strain effects on charge carrier confinement in Ge${}_{x}$Si${}_{1\ensuremath{-}x}$ quantum dots (QDs) grown on an oxidized Si surface. The strain and free carrier probability density distributions are obtained using the continuum elasticity theory and the effective-mass approximation implemented by a finite-element modeling scheme. Using realistic parameters and conditions for hemisphere and pyramid QDs, it is pointed out that an uncapped hemisphere dot deposited on the Si surface with an intermediate ultrathin oxide layer offers advantageous electron-hole separation distances with respect to a square-based pyramid grown directly on Si. The enhanced sep…
Toward an Understanding of the Catalytic Role of Hydrogen-Bond Donor Solvents in the Hetero-Diels−Alder Reaction between Acetone and Butadiene Deriva…
2006
A detailed theoretical investigation of the catalytic role of hydrogen-bond- (HB-) donor molecules (water, methanol, chloroform, dichloromethane, and chloromethane) in the hetero-Diels-Alder reaction between acetone and N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene is presented. This work extends a previous study (Domingo, L. R.; Andres, J. J. Org. Chem. 2003, 68, 8662) in which the importance of weak HB-donor solvents to catalyze more effectively than solvents with a higher dielectric constant but no HB-donor capability was analyzed. Now, based on density functional theory (DFT) at B3LYP/6-31+G(d) level calculations, different techniques for analyzing the nature of HB interaction, namely, n…
Understanding the mechanism of non-polar diels-alder reactions. A comparative elf analysis of concerted and stepwise diradical mechanisms
2010
The electron-reorganization along the concerted and stepwise pathways associated with the non-polar Diels-Alder reaction between cyclopentadiene (Cp, 1) and ethylene (2) has been studied using the topological analysis of the electron localization function (ELF) at the B3LYP/6-31G(d) level of theory. ELF results for the concerted mechanism stresses that the electron-reorganization demanded on the diene and ethylene reagents to reach two pseudo-diradical structures is responsible for the high activation energy. A comparative ELF analysis of some relevant points of the non-polar Diels-Alder reaction between Cp and styrene (10) suggests that these concerted mechanisms do not have a pericyclic e…
Azo-hydrazo conversion via [1,5]-hydrogen shifts. A combined experimental and theoretical study
2012
Abstract Azoalkenes 6e , 6g , 6h , and 8c underwent an easy azo-hydrazo conversion via a [1,5]-hydrogen shift yielding α,β-unsaturated hydrazones. The isomerization products were characterized through spectroscopic and spectrometric techniques. In order to understand the nature of the mechanism of these [1,5]-hydrogen shifts, the transition state structures of the reactions were theoretically studied at the B3LYP/6-31G(d,p) level. Substitution effects in the propenylazo system on the kinetic and thermodynamic parameters were analyzed. An electron localization function (ELF) analysis of the electronic structure of the transition state structure associated with the azo-hydrazo conversion of t…
When are thin films of metals metallic? Part III
1996
Abstract A large amount of experimental information has indicated that very thin films of metallic elements can exhibit nonmetallic behavior, even on metal substrates. These films undergo a gradual nonmetal to metal transition with increasing film density or thickness. The nonmetallic behavior can be related to electron localization due to strong electron-electron correlation in low dimensional systems, as indicated by the strong enhancement of electron effective mass. The evolution in the electronic structure associated with the nonmetal to metal transition bears a striking resemblance to the behavior observed for free metal clusters. Part I [1], outlined the general concepts of a nonmetal…
Energy spectrum, persistent current and electron localization in quantum rings
2003
Energy spectra of quasi-one-dimensional quantum rings with a few electrons are studied using several different theoretical methods. Discrete Hubbard models and continuum models are shown to give similar results governed by the special features of the one-dimensionality. The energy spectrum of the many-body system can be described with a rotation-vibration spectrum of a 'Wigner molecule' of 'localized' electrons, combined with the spin-state determined from an effective antiferromagnetic Heisenberg Hamiltonian. The persistent current as a function of magnetic flux through the ring shows periodic oscillations arising from the 'rigid rotation' of the electron ring. For polarized electrons the …