Investigation of Halogen Bond Interactions of Chiral Molecules Using Infrared, Vibrational Circular Dichroism, NMR, UV-vis Spectroscopy and Density Functional Theory Calculations

Abstract

This PhD thesis shows the application of different spectroscopic and theoretical tools to probe the extent and possible interaction between various Lewis acids (halogen bond donor) and Lewis bases (halogen bond acceptors). Vibrational circular dichroism (VCD) that is the chiral version of infrared (IR) spectroscopy is able to provide valuable information about the absolute configuration of a chiral molecule in the solution when coupled with theoretical calculations. This technique is also sensitive to intermolecular interactions. Since the strength and level of interaction between the halogen bond donors and halogen bond acceptors is unknown to us we have also decided to utilize other spectroscopy techniques such as 19F-NMR, 1HNMR, and UV-vis spectroscopy. In chapter 3, I studied the formation of the halogen bond between 4-benzyl- 1,3-thiazolidine-2-one (NOS) and iodine. In order to probe the interaction between the two molecules I used FT-IR, VCD, 1H-NMR, and UV-vis spectroscopy techniques. Density Functional Theory (DFT) calculations allowed me to find out what would be the conformers of the interacting species and which ones would contribute to the formation of final complexes. This study concluded with no interaction between the two species. In chapter 4, I studied the formation of the halogen bond between 4-benzyl- 1,3-thiazolidine-2-thione (NSS) and iodine in the solution using FT-IR, VCD, 1HNMR, and UV-vis spectroscopy techniques. DFT simulations were carried out to find out the most stable conformers of the interacting species and the formation of final complexes. This study concluded with discovery of a new halogen bond interaction motif between the two species. In chapter 5, I studied the formation of halogen bond between 4-benzyl-1,3- thiazolidine-2-one (NOS) and iodopentafluorobenzene (F5BnI) in the solution using FT-IR, VCD, 1H-NMR, and 19F-NMR spectroscopy. Sensitivity of the VCD and 19FNMR spectroscopy allowed me to monitor small changes in the spectra of interacting species. Consequently with the aid of DFT simulations I was able to suggest the most probable conformer for the interaction between the donor and acceptor species. In chapter 6, I studied the formation of halogen bond between 4-benzyl-1,3- thiazolidine-2-thione (NSS) and iodopentafluorobenzene (F5BnI) in the solution using FT-IR, VCD, 1H-NMR, and 19F-NMR spectroscopy. 19F-NMR signals does not suggest a strong interaction between the two species due to the low change in the chemical shift. Despite the fact that the interaction between these species is weak, we were able to collect signals from the VCD machine which together with the DFT data enabled us to suggest a possible structure in the formation of the complex.