TY - JOUR
T1 - Steric Effects of Solvent Molecules on SN2 Substitution Dynamics
AU - Liu, Xu
AU - Xie, Jing
AU - Zhang, Jiaxu
AU - Yang, Li
AU - Hase, William L.
N1 - Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/4/20
Y1 - 2017/4/20
N2 - Influences of solvent molecules on SN2 reaction dynamics of microsolvated F-(H2O)n with CH3I, for n = 0-3, are uncovered by direct chemical dynamics simulations. The direct substitution mechanism, which is important without microsolvation, is quenched dramatically upon increasing hydration. The water molecules tend to force reactive encounters to proceed through the prereaction collision complex leading to indirect reaction. In contrast to F-(H2O), reaction with higher hydrated ions shows a strong propensity for ion desolvation in the entrance channel, diminishing steric hindrance for nucleophilic attack. Thus, nucleophilic substitution avoids the potential energy barrier with all of the solvent molecules intact and instead occurs through the less solvated barrier, which is energetically unexpected because the former barrier has a lower energy. The work presented here reveals a trade-off between reaction energetics and steric effects, with the latter found to be crucial in understanding how hydration influences microsolvated SN2 dynamics.
AB - Influences of solvent molecules on SN2 reaction dynamics of microsolvated F-(H2O)n with CH3I, for n = 0-3, are uncovered by direct chemical dynamics simulations. The direct substitution mechanism, which is important without microsolvation, is quenched dramatically upon increasing hydration. The water molecules tend to force reactive encounters to proceed through the prereaction collision complex leading to indirect reaction. In contrast to F-(H2O), reaction with higher hydrated ions shows a strong propensity for ion desolvation in the entrance channel, diminishing steric hindrance for nucleophilic attack. Thus, nucleophilic substitution avoids the potential energy barrier with all of the solvent molecules intact and instead occurs through the less solvated barrier, which is energetically unexpected because the former barrier has a lower energy. The work presented here reveals a trade-off between reaction energetics and steric effects, with the latter found to be crucial in understanding how hydration influences microsolvated SN2 dynamics.
UR - http://www.scopus.com/inward/record.url?scp=85018529684&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.7b00577
DO - 10.1021/acs.jpclett.7b00577
M3 - Article
C2 - 28394615
AN - SCOPUS:85018529684
SN - 1948-7185
VL - 8
SP - 1885
EP - 1892
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 8
ER -