Banca de DEFESA: CARLOS VITAL DOS SANTOS JÚNIOR

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : CARLOS VITAL DOS SANTOS JÚNIOR
DATE: 29/10/2021
TIME: 08:30
LOCAL: VIDEOCONFERÊNCIA
TITLE:

Electronic structure and chemical bonds in mechanisms of chemical reactions of nucleophilic substitution: Topological analyses of total and overlap electronic density

KEY WORDS:

QTAIM, LVM, Overlap properties, spectator bond, S_N2.

PAGES: 81
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Química Teórica
SUMMARY:

Understanding the key aspects of chemical reaction mechanisms is usually focused on the profile energetic surface (PES) energetic and structural. However, bond analysis methodologies can add information about the reaction mechanisms. An attractive reaction to apply bond analysis methods is the bimolecular nucleophilic substitution (S_N2). A peculiar feature of this reaction in the gas phase is the PES dependence on the atomic center and/or substituent group nature, generally attributed to steric effects. The central goal of this work is to apply the QTAIM, overlap properties (OP), and local vibrational mode (LVM) theory models to study the chemical bonds in stationary points of the Cl^– + XR₃Cl (with A = C and Si) and C^–– + BR₂Cl (with B = P and N) reactions, with R = H, F, Cl, Me, e Et. On the one hand, for the S_N2@C and S_N2@N reactions, the reactants and products are separated by a pentacoordinate(@C) and tetracoordinate (@N) transition state (TS), corresponding to a saddle point in the PES. On the other hand, for S_N2@Si and S_N2@P reactions a stable pentacoordinate(@Si) and tetracoordinate (@P) transition complex is observed. The chemical bond descriptors  and , overlap properties () and LVM force constants () were obtained for the studied systems. QTAIM analysis indicated that the C–R and N–R bonds are indicated to be more covalent than the Si–R and P–R bonds, due more negative H_BCP and  values. These results agree with the overlap properties to C–R and N–R bonds, indicating a high density concentration as compared to Si–R and P-R bonds. Besides, the LVM analysis also reveal that the C–R and N–R bonds are more stronger (from the force constants  values) than Si–R and P–R ones. Lastly, the overlap Coulomb repulsion energy () is generally greater in C–R than in Si–R in XR₃Cl systems, suggesting that the steric hindrance experienced by Cl^– in S_N2@C reactions is probably associated with the greater covalent nature of C–R bonds, that concentrate density along the chemical bond more efficiently than in Si–R.

 

BANKING MEMBERS:
Interno - 1086214 - ANDERSON DOS REIS ALBUQUERQUE
Externo à Instituição - JÚLIO COSME SANTOS DA SILVA - UFAL
Presidente - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Externo à Instituição - RENALDO TENÓRIO DE MOURA JÚNIOR - UFPB