TY - JOUR
T1 - Facile SN2 reaction in protic solvent
T2 - Quantum chemical analysis
AU - Oh, Young Ho
AU - Ahn, Doo Sik
AU - Chung, Sang Yoon
AU - Jeon, G. Hwan
AU - Park, Sung Woo
AU - Oh, Seung Jun
AU - Kim, Dong Wook
AU - Kil, Hee Seup
AU - Chi, Dae Yoon
AU - Lee, Sungyul
PY - 2007/10/11
Y1 - 2007/10/11
N2 - 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].
AB - 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].
UR - http://www.scopus.com/inward/record.url?scp=35549007218&partnerID=8YFLogxK
U2 - 10.1021/jp0743929
DO - 10.1021/jp0743929
M3 - Article
C2 - 17880052
AN - SCOPUS:35549007218
SN - 1089-5639
VL - 111
SP - 10152
EP - 10161
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 40
ER -