Facile SN2 reaction in protic solvent: Quantum chemical analysis

Young Ho Oh, Doo Sik Ahn, Sang Yoon Chung, G. Hwan Jeon, Sung Woo Park, Seung Jun Oh, Dong Wook Kim, Hee Seup Kil, Dae Yoon Chi, Sungyul Lee

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

We study the effects of protic solvent (water, methanol, ethanol, and tert-butyl alcohol) and cation (Na+, K+, Cs+) on the unsymmetrical SN2 reaction X- + RY → RX + Y- (X = F, Br; R = CH3,C3H7;Y = Cl, OMs). We describe a series of calculations for the SN2 reaction mechanism under the influence of cation and protic solvent, presenting the structures of pre- and postreaction complexes and transition states and the magnitude of the activation barrier. An interesting mechanism is proposed, in which the protic solvent molecules that are shielded from the nucleophile by the intervening cation act as a Lewis base to reduce the unfavorable Coulombic influence of the cation on the nucleophile. We predict that the reaction barrier for the SN2 reaction is significantly lowered by the cooperative effects of cation and protic solvent. We show that the cation and protic solvent, each of which has been considered to retard the SN2 reactivity of the nucleophile, can accelerate the reaction tremendously when they interact with the fluoride ion in an intricate, combined fashion. This alternative SN2 mechanism is discussed in relation to the recently observed phenomenal efficiency of fluorination in tert-alcohol media [Kim, D. W.; et al. J. Am. Chem. Soc. 2006, 128, 16394].

Original languageEnglish
Pages (from-to)10152-10161
Number of pages10
JournalJournal of Physical Chemistry A
Volume111
Issue number40
DOIs
StatePublished - 11 Oct 2007

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