%0 DATA
%A Hua, Fang
%A Yongho, Kim
%D 2013
%T Excited-State Tautomerization of 7‑Azaindole
in Nonpolar Solution: A Theoretical Study Based on Liquid-Phase Potential
Surfaces of Mean Force
%U https://acs.figshare.com/articles/journal_contribution/Excited_State_Tautomerization_of_7_Azaindole_in_Nonpolar_Solution_A_Theoretical_Study_Based_on_Liquid_Phase_Potential_Surfaces_of_Mean_Force/2387911
%R 10.1021/ct3010694.s001
%2 https://acs.figshare.com/ndownloader/files/4027603
%K proton transfer
%K integral equation formalism
%K VTST
%K adiabatic energy surfaces
%K KIE
%K CASSCF
%K HH
%K variational transition state theory
%K MRPT
%K multireference perturbation theory
%K ForceExcited state tautomerization
%K SMD
%K IEFPCM
%K tunneling
%K electron correlation
%K polarizable continuum model
%K TS
%K dielectric continuum model
%K 7 AI
%X Excited state tautomerization of
a 7-azaindole (7AI) complex with
one methanol molecule in heptane was studied using variational transition
state theory including multidimensional tunneling (VTST/MT) with the
dielectric continuum model for the solvent effect. Electronic structures
and energies for reactants and transition state (TS) in solution were
computed at the complete active space self-consistent field (CASSCF)
level with second-order multireference perturbation theory (MRPT2)
to take into consideration of dynamic electron correlation. The polarizable
continuum model using the integral equation formalism (IEFPCM) and
the SMD model were used for the excited-state solvent effect. Excited-state
surfaces of potential of the mean force in solution were generated
for the first time at the MRPT2//SMD/CASSCF(10,9)/6-31G(d,p) level.
The position of TS on the reaction coordinate substantially depended
on the dynamic electron correlation. The two protons in the excited-state
tautomerization were transferred in a concerted but asynchronous process.
Calculated HH/DD kinetic isotope effect (KIE) and the ratio of Arrhenius
pre-exponential factors, *A*(HH)/*A*(DD), agreed very well with the corresponding experimental values.
The shape of the adiabatic energy surfaces in the excited-state strongly
depended on the position of isotopes due to the asynchronicity of
the reaction path, and the tunneling effect was essential for reproducing
experimental KIEs. The pyrrolic proton moved a twice longer distance
by tunneling than the hydroxyl proton in the most probable tunneling
path at 292 K. This study strongly suggests that the mechanism of
the excited-state double proton transfer in heptane is triggered by
proton transfer from the pyrrolic nitrogen of 7AI to alcohol (protolytic
pathway), rather than by proton transfer from alcohol to the pyridine
nitrogen of 7AI (solvolytic pathway).