Ion pair aggregates and reactions; experiment and theory

Origin of Enhanced Reactivity of a Microsolvated Nucleophile in Ion Pair SN2 Reactions: The Cases of Sodium p-Nitrophenoxide with Halomethanes in Acetone

“…The previous studies , disclosed that one to four solvent molecules can coordinate on the alkali metal. Therefore, herein we introduce a microsolvation model constructed by one to three explicit acetone molecules and sodium p -nitrophenoxide to study the S N 2 reaction in pure acetone, in which the sodium atom is coordinated by one to three oxygen atom(s) on acetone (see Figure ).…”

“…In this case, the dominant nucleophilic species will be ion pairs instead of free ions . Actually, many important organic reactions as well as biological processes usually involve neutral ion pairs as nucleophiles. − In recent years, the ion pair reaction has received increasing attention since its application has been discovered in the field of phase-transfer catalysis …”

“…It is well know that the reactivity of an ion pair nucleophile is rather different from that of an anionic one, ,− and theoretical investigations of ion pair S N 2 reactions are relatively scarce. − ,− Two different reaction pathways were proposed for the ion pair S N 2 reactions in the gas phase, i.e., backside attack with inversion and frontside attack with retention of configuration. Both pathways are preceded via cyclic, highly strained transition states (TSs), leading to a higher reaction barrier than for the corresponding anionic reaction in the gas phase. ,,,, This result can be explained by the much weaker basicity of the neutral ion pair than of the free anionic nucleophile induced from partially neutralized nucleophile by counterion.…”