Siklopropenyum aktivasyonlu SN2 tepkime mekanizmalarının aydınlatılması: Hesapsal bir yaklaşım

Nucleophilic substitution of alcohols has a strategic importance in organic chemistry due to their wide usage in pharmaceutical industry. Despite the importance of these reactions, the traditional reagents used in the experimental studies suffer several problems including poor reactivity, hazardous by-product formation, narrow scope product formation. In 2009, as a powerful alternative to the established methods, Lambert et al. whom provides a support from a pharmaceutical industry, developed a new method for the nucleophilic substitution of alcohols. The new method based on the formation of cyclopropenium cation in situ and the activation of alcohol containing substrates through the usage of this reagent. They have demonstrated the effectiveness of this new methodology in a number of dehydration reactions including, chlorodehydration, diolcyclodehydration and Beckmann Rearrangement reactions. Cyclopropenones were first prepared by Breslow and Volpin in 1959 which are stable precursor to cyclopropenium ions. These compounds have a number of useful qualities for applications in catalysis, which include the ability to be polarizable due to aromatic resonance form and to tune their physical and electronic properties. Despite being widespread usage, the mechanisms that they involved are not clarified yet. In this project, comprehensive density functional theory calculations were carried out to explain the experimentally proposed reaction mechanisms for chlorodehydration and Beckmann rearrangement reactions. The geometrical structures of all stationary points in the energy profile were optimized by employing the M062X functional and the 6-31+G(d,p) basis. In addition, benchmark studies were done with different functionals, methods and basis sets to validate the methodology used in the study. The results pointed out that temperature factor takes an important role in determination of Beckmann rearrangement reaction mechanisms. Further, the alterations in the oxime and cyclopropene ring substitutents have an impact on the efficiency of the reaction. In conclusion, in chlorodehydration reactions, preferred mechanism depends on the substituents on the phenyl ring of the cyclopropenone and the results enabled us to explain the product distribution in that reactions.