Theoretical studies orbital interaction analysis

Complexes with one and two amines are common. For example, bis-(trimethylamine) alane, A1H3(N(CH3)3)2, is a white crystalline solid with a low vapor pressure. Using ammonia as a model for trimethylamine, apply orbital interaction analysis to describe the bonding in the 1 1 and 1 2 complexes. Theoretical studies on the ammonia complexes of AIH3 have led to the conclusion that there is little dative bonding (as judged by the amount of charge transfer) (Marsh, C. M, B. Schaefer III, H. F., J. Phys. Chem., 1995, 99, 14309-14315). Comment on the theoretical results. 

Other theoretical studies discussed above include investigations of the potential energy profiles of 18 gas-phase identity S 2 reactions of methyl substrates using G2 quantum-chemical calculations," the transition structures, and secondary a-deuterium and solvent KIEs for the S 2 reaction between microsolvated fluoride ion and methyl halides,66 the S 2 reaction between ethylene oxide and guanine,37 the complexes formed between BF3 and MeOH, HOAc, dimethyl ether, diethyl ether, and ethylene oxide,38 the testing of a new nucleophilicity scale,98 the potential energy surfaces for the Sn2 reactions at carbon, silicon, and phosphorus,74 and a natural bond orbital-based CI/MP through-space/bond interaction analysis of the S 2 reaction between allyl bromide and ammonia.17... 

Although, as stated above, olefin epoxidation is commonly referred to as an electrophilic oxidation, recent theoretical calculations suggest that the electronic character of the oxygen transfer step needs to be considered to fully understand the mechanism [451]. The electronic character, that is, whether the oxidant acts as an electrophile or a nucleophile is studied by charge decomposition analysis (CDA) [452,453]. This analysis is a quantitative interpretation of the Dewar-Chatt-Dimcanson model and evaluates the relative importance of the orbital interactions between the olefin (donor) and the oxidant (acceptor) and vice versa [451]. For example, dimethyldioxirane (DMD) is described as a chameleon oxidant because in the oxidations of acrolein and acrylonitrile, it acts as a nucleophile [454]. In most cases though, epoxidation with peroxides occurs predominantly by electron donation from the 7t orbital of the olefin into the a orbital of the 0-0 bond in the transition state [455,456] (Fig. 1.10), so the oxidation is justifiably called an electrophilic process. 

The interaction of a Pd4 (C4v) cluster with the oxide surface was analyzed in more detail with the help of electron density difference plots and other theoretical tools, such as population analysis, core level shifts as well as induced and dynamic dipole moments [175]. Three interaction mechanisms were found to contribute to different extent metal polarization with the subsequent electrostatic attraction, Pauli repulsion, and covalent orbital interactions. Electrostatic interactions make up a sizeable fraction of the adhesion energy the polarization of the metal adsorbate by the surface electric field provides an important bonding mechanism. For the adsorption of Pd on-top or in the vicinity of the surface Mg " cations this electrostatic interaction accounts for almost the entire adsorption energy, albeit counteracted by Pauli repulsion. For adsorption on-top 0 , on the other hand, mixing of adsorbate and substrate orbitals becomes noticeable. This hybridization or covalent bonding at the interface with the oxide anions is complemented by electrostatic polarization. Further work is required to establish in a more quantitative way the relative importance of electrostatic and chemical bonding contributions. However, in line with our other studies of... 

Both experimental and theoretical studies of the seven-membered zirconacyclo-cumulenes have been reported [43, 45, 46]. The stability of the seven-membered zirconacyclocumulene has been ascribed to the interaction between one of the Zr t/ orbital with one terminal a orbital and the in-plane ti orbital of the cumulene, forming a type covalent bonding interaction [46]. The molecule orbital analysis shown in Fig. 8 is consistent with this conclusion (Fig. 8, HOMO-2). In HOMO-4, the Zr orbital overlaps with the sp hybridized orbital of Cl, forming the Zr-Cla covalent bond. 

Fujknoto, H. Yamasaki, T. Mizutani, H. Koga, N. A theoretical study of olefin insertions into Ti-C and Ti-H Bonds. An analysis by paired interacting orbitals. J. Am. Chem. Soc. 1985, 107, 6157-6161. 

Several theoretical investigations described the interaction of a d° metal center with a peroxide in order to understand oxygen transfer from a TM center to an alkene [2, 39-42] or a sulfide [43], These studies, using semiempirical methods or the ab initio Hartree-Fock SCI method, were limited to an orbital analysis ofthe ground state of metal peroxides. 

The most extensive and systematic study of the chemistry of lignin with theoretical methods has been performed by Remko and co-workers. Their work has involved the nature of intramolecular (40-43) and inter-molecular (44-48) hydrogen bonding of lignin model compounds, spectral transitions (49-52), and conformational analysis (53). The methods used have included CNDO/2 and PCILO (Perturbative Configuration Interaction using Localized Orbitals) (54). 

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