Navegando por Autor "Antunes, Octávio Augusto Ceva"
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Artigo Derivatives of spiropentadiene dication: New species with planar tetracoordinate carbon (ptC) atom(American Chemical Society, 2009-03-11) Firme, Caio Lima; Antunes, Octávio Augusto Ceva; Esteves, Pierre Mothé; Corrêa, Rodrigo JoséIn this work, nine tetrasubstituted derivatives [NH2, OCH3, Li, Na, Si(CH3)3/SiH2CH3, P(CH3)2, Cl, F, and CN] of the spiropentadiene dication were analyzed within the framework of QTAIM. In the studied series, the electron-withdrawing substituents destabilize the ptC-containing spiropentadiene dication. On the other hand, stabilization of this dication is possible for electron-donating substituents only through σ bonds, such as Li and Na. In all studied systems, according to QTAIM, the π-electron system does not participate in the stabilization of the ptC atom in the spiropentadiene dication. σ-electron-donating groups stabilize the spiropentadiene dication system by increasing the charge density of Cext—ptC bonds, whereas electron-withdrawing groups remove the charge density from Cext—ptC bonds.Artigo Relation between bond order and delocalization index of QTAIM(Elsevier, 2009-01-22) Firme, Caio Lima; Antunes, Octávio Augusto Ceva; Esteves, Pierre MothéThe formal bond order is half the difference between the number of bonding and anti-bonding electrons. The relation between delocalization index (DI) from QTAIM and formal bond order is linear for CC, NN, GeGe, C–Si, C–Ge and CN bonds. The electronegativity is closely related with the correspondence between the DI and the formal bond order for the CC, NN and GeGe bonds. By using the electronegativity of C, N and Ge atoms, it was obtained a general relation between the formal bond order and the DI for CC, NN and GeGe atomic pairs.Artigo Topological study of bis (cyclopentadienyl) titanium and bent titanocenes(Elsevier, 2010-10-29) Firme, Caio Lima; Pontes, Daniel de Lima; Antunes, Octávio Augusto CevaThe electronic nature of ferrocene, titanocene and some bent titanocenes was analyzed by QTAIM. PBE1PBE-optimised geometrical data agreed well with X-ray diffraction data, this method being chosen to extract and analyze the wave functions of all studied metallocenes within the QTAIM framework. Within the studied metallocenes, the number of bond paths can be used as an indicative of their stability. The Ind2Ti(CH3)2 has less Ti–C bond paths than the Cp2Ti(CH3)2 as well as the Cp2Ti has less C–Mt bond paths than Cp2Fe. These results concords with the smaller stabilities of Ind2Ti(CH3)2 and Cp2Ti relative to their counterparts.