title: Origin of Enhanced Reactivity of a Microsolvated Nucleophile in Ion Pair SN2 Reactions: The Cases of Sodium p-Nitrophenoxide with Halomethanes in Acetone.
abstract: In a kinetic experiment on the SN2 reaction of sodium p-nitrophenoxide with iodomethane in acetone-water mixed solvent, Humeres et al. (J. Org. Chem. 2001, 66, 1163) found that the reaction depends strongly on the medium, and the fastest rate constant was observed in pure acetone. The present work tries to explore why acetone can enhance the reactivity of the title reactions. Accordingly, we make a mechanistic study on the reactions of sodium p-nitrophenoxide with halomethanes (CH3X, X = Cl, Br, I) in acetone by using a supramolecular/continuum model at the PCM-MP2/6-311+G(d,p)//B3LYP/6-311+G(d,p) level, in which the ion pair nucleophile is microsolvated by one to three acetone molecules. We compared the reactivity of the microsolvated ion pair nucleophiles with solvent-free ion pair and anionic ones. Our results clearly reveal that the microsolvated ion pair nucleophile is favorable for the SN2 reactions; meanwhile, the origin of the enhanced reactivity induced by microsolvation of the nucleophile is discussed in terms of the geometries of transition state (TS) structures and activation strain model, suggesting that lower deformation energies and stronger interaction energies between the deformed reactants in the TS lead to the lower overall reaction barriers for the SN2 reaction of microsolvated sodium p-nitrophenoxide toward halomethanes in acetone.
authors.affiliation: †College of Chemistry and Material Science, Sichuan Normal University, Chengdu, 610068, People's Republic of China.
authors.forename: Qiang-Gen
authors.initials: QG
authors.lastname: Li
authors.affiliation: ‡School of Chemistry and Pharmaceutical Engineering, Sichuan University of Science and Engineering, Zigong, 643000, People's Republic of China.
authors.forename: Ke
authors.initials: K
authors.lastname: Xu
authors.affiliation: §College of Chemistry and Key State Laboratory of Biotherapy, Sichuan University, Chengdu 610064, People's Republic of China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Ren
mesh_terms: D000096:Acetone / Q000737:chemistry*; D006847:Hydrocarbons, Iodinated / Q000737:chemistry*; D009574:Nitro Compounds / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D011789:Quantum Theory; D014867:Water / Q000737:chemistry
chemical_list: D006847:Hydrocarbons, Iodinated; D009574:Nitro Compounds; D010636:Phenols; D014867:Water; D000096:Acetone; C014055:methyl iodide