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The relationship between 2J(CH) coupling and relative stereochemistry

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Bruna Rogério de Abreu
Total Authors: 1
Document type: Master's Dissertation
Press: Campinas, SP.
Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
Defense date:
Examining board members:
Cláudio Francisco Tormena; Denize Cristina Favaro; Armando Juan Navarro Vázquez
Advisor: Cláudio Francisco Tormena

The 2JCH geminal coupling has been applied as a tool for determining the stereochemistry since its magnitude and sign observed provide essential information about molecular relative orientation. Thus, this study theoretically evaluates the stereoelectronic factors responsible for the variation of sign and magnitude in the 2JCH coupling for the successive addition of the X groups in the olefinic system leading to mono-, di- and trisubstituted derivatives with X groups (X = Cl, Br, I, CH3, CN, OH, and NH2). To achieve this goal, the geometries were optimized with M06-2X/TZ2P level of theory. For a better description of the systems under study, preliminary calibration of DFT functionals taking disubstituted isomers of chlorine and bromine as the molecular model system was carried out in order to determine the level of theory providing more consistent results in comparison with experimental measurements. Therefore, different combinations of functionals (B3LYP, PBE0, and BHandH), basis set (TZ2P, TZ2P-J, QZ4P, QZ4P-J, and JCPL), the influence of the solvent (chloroform) was evaluated using implicit solvation with COSMO model were tested and relativistic effects via the spin-orbit ZORA Hamiltonian were considered. The best condition for theoretical calculations was obtained using PBE0/TZ2P level of theory. The experimental geminal coupling was measured applying PIP-HSQMBC-IPAP pulse sequence. After determining experimental and theoretical 2JCH values, the main orbitals involved in the sign and magnitude of 2JCH were evaluated through decomposition analysis of 2JCH into natural localized molecular orbital (NLMO) contributions. The energies (E2/EX) involved in the main orbitals were also used to determine the transmission pathway. The results suggest that the sign and magnitude of 2JCH are dictated by the relative orientation of hydrogen concerning the X groups and the number of X groups in the molecule. Similar behavior was obtained for chlorine, bromine, iodine, and amino derivatives, while for alkyl, cyano, and hydroxyl groups no correlation between them was observed (AU)

FAPESP's process: 18/17818-0 - Evaluation of the effects involved in the relation between 2JCH coupling constant and relative stereochemistry
Grantee:Bruna Rogério de Abreu
Support Opportunities: Scholarships in Brazil - Master