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A Study of Weak Noncovalent Interactions

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2005, Doctor of Philosophy, Miami University, Chemistry and Biochemistry.
Noncovalent weak interactions such as pi-pi, lone pair-pi and C-H...O hydrogen bonding have been studied experimentally. Triptycene-derived model compounds serves as conformational equilibrium reporters for direct measurements of these interactions. For arene-arene interactions in the parallel-displaced orientation, a series of triptycene derivatives bearing 1, 9- arenes with different substituents were synthesized and the ratios of syn to anti conformers were determined in terms of low-temperature NMR spectroscopy. The free energies of the interactions were then derived from the syn/anti ratios. Two possible mechanisms are suggested for off-set arene-arene interactions. For the systems with a moderate electron donor and electron acceptor, electrostatic forces are believed to control the arene-arene interactions. The interactions between the arenes bearing electron-donating groups (EDG) are found to be either negligible or slightly repulsive, while the interactions between arenes with electron-withdrawing groups (EWG) are attractive. However, for the systems with one strong electron acceptor such as pentafluorophenyl, the interactions are found always attractive regardless of whether the other arene has EWG or not. Furthermore, the interactions between the arenes bearing EDG and EWG are much stronger than those between arenes both bearing EWG. Therefore, charge-transfer interactions are proposed to play a significant role in these systems. Moreover, off-centered lone pair-arene interactions and C-H...O hydrogen bond interactions are also investigated by triptycene-derived systems successfully. The results are consistent with theoretical calculations. Noncovalent interactions have also been studied by computational chemistry. The driving forces in controlling the stereoselection for two allylboration reactions have been explored. For the Roush allylboration, the interactions between the aldehyde carbonyl carbon and the carbonyl oxygen of tartrate ester or amide are found to play significant roles in stabilizing the transition states instead of formyl H-bond based on the results calculated at B3LYP/6-31G* level. For the allylation of a-methoxy-propanal by allylboronic acid, an ab initio MO study shows that the Cornforth-like transition state is more stable than the Felkin-Anh transition state.
Benjamin Gung (Advisor)
196 p.

Recommended Citations

Citations

  • Xue, X. (2005). A Study of Weak Noncovalent Interactions [Doctoral dissertation, Miami University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=miami1127093969

    APA Style (7th edition)

  • Xue, Xiaowen. A Study of Weak Noncovalent Interactions. 2005. Miami University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=miami1127093969.

    MLA Style (8th edition)

  • Xue, Xiaowen. "A Study of Weak Noncovalent Interactions." Doctoral dissertation, Miami University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1127093969

    Chicago Manual of Style (17th edition)