title: Applications of the ETS-NOCV method in descriptions of chemical reactions.
abstract: The present study characterizes changes in the electronic structure of reactants during chemical reactions based on the combined charge and energy decomposition scheme, ETS-NOCV (extended transition state-natural orbitals for chemical valence). Decomposition of the activation barrier, ΔE (#), into stabilizing (orbital interaction, ΔE (orb), and electrostatic, ΔE (elstat)) and destabilizing (Pauli repulsion, ΔE (Pauli), and geometry distortion energy, ΔE (dist)) factors is discussed in detail for the following reactions: (I) hydrogen cyanide to hydrogen isocyanide, HCN → CNH isomerization; (II) Diels-Alder cycloaddition of ethene to 1,3-butadiene; and two catalytic processes, i.e., (III) insertion of ethylene into the metal-alkyl bond using half-titanocene with phenyl-phenoxy ligand catalyst; and (IV) B-H bond activation catalyzed by an Ir-containing catalyst. Various reference states for fragments were applied in ETS-NOCV analysis. We found that NOCV-based deformation densities (Δρ (i)) and the corresponding energies ΔE (orb)(i) obtained from the ETS-NOCV scheme provide a very useful picture, both qualitatively and quantitatively, of electronic density reorganization along the considered reaction pathways. Decomposition of the barrier ΔE(#) into stabilizing and destabilizing contributions allowed us to conclude that the main factor responsible for the existence of positive values of ΔE (#) for all processes (I, II, III and IV) is Pauli interaction, which is the origin of steric repulsion. In addition, in the case of reactions II, III and IV, a significant degree of structural deformation of the reactants, as measured by the geometry distortion energy, plays an important role. Depending on the reaction type, stabilization of the transition state (relatively to the reactants) originating either from the orbital interaction term or from electrostatic attraction can be of vital importance. Finally, use of the ETS-NOCV method to describe catalytic reactions allows extraction of information on the role of catalysts in determination of ΔE (#).
authors: Department of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060, Krakow, Poland. mitoraj@chemia.uj.edu.pl
authors: Mariusz Paweł
authors: MP
authors: Mitoraj
authors: Monika
authors: M
authors: Parafiniuk
authors: Monika
authors: M
authors: Srebro
authors: Michał
authors: M
authors: Handzlik
authors: Agnieszka
authors: A
authors: Buczek
authors: Artur
authors: A
authors: Michalak
mesh_terms: D000465:Algorithms; D001880:Boranes / Q000737:chemistry; D002070:Butadienes / Q000737:chemistry; D002384:Catalysis; D003198:Computer Simulation; D003485:Cyanates / Q000138:chemical synthesis; D004583:Electrons; D005030:Ethylenes / Q000737:chemistry; D006856:Hydrogen Cyanide / Q000737:chemistry; D007536:Isomerism; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry; D011789:Quantum Theory; D055672:Static Electricity; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D001880:Boranes; D002070:Butadienes; D003485:Cyanates; D005030:Ethylenes; D009942:Organometallic Compounds; C406884:titanocene; D006856:Hydrogen Cyanide; C036216:ethylene; C031763:1,3-butadiene; C005057:isocyanic acid