The nucleophilic aromatic substitution reaction (SNAr) between pyrrolidine, piperidine, and morpholine with 2-L-5-nitrothiophene and2-L-3-nitrothiophene have been examined in the room temperature ionic liquids (RTILs) [BMIM][BF4] and [BMIM][PF6]; BMIM = 1-butyl-3-methylimidazolium cation and L = leaving groups bromine, methoxy, phenoxide and para-nitrophenoxide. RTILs posses a 3D polymeric network of anions and cations formed from strong ion-ion interactions creating a unique and complex reaction environment. QM/MM/MC/FEP calculations were performed to elucidate the IL effect upon the reaction rate and mechanism relative to the conventional organic solvent methanol. The enhanced rates originating from the solvent effects may be attributed to the less extensive solvation of the nucleophile and the extensive hydrogen-bond donor and hydrogen-bond acceptor capabilities of the ILs. The present calculations shed light on the unique impact of ILs upon the SNAr reactions via increased stabilization of the Meisenheimer intermediate complex and the transition structures.

Solvent effects of ionic liquids on the aromatic nucleophilic substitution reaction from QM/MM simulations

245th National Meeting (2013)

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