Frontier Molecular Orbital Study for the Reaction of Tresyl Chloride

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In the current studies, we used frontier molecular orbital theory to understand the coupling reaction of tresyl chloride (Cl-SO_2CH_2CF_3)-activated titanium and fibronectin. Because titanium contains a large number of basic functions, it is impossible to calculate the molecular orbital of titanium. Therefore, we used methanol as model compound for calculations. Semi-empirical determinations of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for methanol, tresyl chloride, tresylated methanol, and methyl amine were obtained using PM3 Hamiltonian calculations. We found that energy difference between the HOMO of methanol and the LUMO of tresyl chloride (9.004 eV) is smaller than that between the LUMO of methanol and the HOMO of tresyl chloride (15.855 eV). This suggests that the reaction of tresyl chloride and methanol is dominated by the interaction of the HOMO of methanol and LUMO of tresyl chloride. In addition, the energy difference between the LUMO of tresylated methanol and HOMO of methyl amine (8.559 eV) is smaller than that between the LUMO of methanol and HOMO of methyl amine (12.909 eV). Therefore, the nucleophilic reaction of methyl amine towards tresylated methanol proceeds more easily than that of the reaction towards methanol. In conclusion, the tresylation of methanol improves its reactivity towards methyl amine by reducing methanol's LUMO energy levels.
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