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Proton‐coupled electron transfer of the phenoxyl/phenol couple: Effect of Hartree‐Fock exchange on transition structures
Author(s) -
Inagaki Taichi,
Yamamoto Takeshi,
Kato Shigeki
Publication year - 2011
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.21892
Subject(s) - proton , hartree–fock method , phenol , chemistry , electron transfer , electron , hartree , computational chemistry , electron exchange , chemical physics , atomic physics , physics , ion , organic chemistry , quantum mechanics
Abstract Proton‐coupled electron transfer (PCET) and hydrogen atom transfer (HAT) reactions of the phenoxyl/phenol couple are studied theoretically by using wave function theory (WFT) as well as DFT methods. At the complete active space self‐consistent field (CASSCF) level, geometry optimization is found to give two transition states (TSs); one is the PCET type with two benzene rings being nearly coplanar, and the other is the HAT type with two benzene rings taking a stacking structure. Geometry optimization at the (semilocal) DFT level, on the other hand, is found to give only one transition state (i.e., the PCET‐type one) and fail to obtain the stacking TS structure. By comparing various levels of theories (including long‐range corrected DFT functionals), we demonstrate that the Hartree‐Fock exchange at long range plays a critical role in obtaining the sufficient stacking stabilization of the present open‐shell system, and that the sole addition of empirical dispersion correction to semilocal DFT functionals may not be adequate for describing such a stacking interaction. Next, we investigate the solvent effect on the PCET and HAT TS thus obtained using the reference interaction site model self‐consistent field (RISM‐SCF) method. The results suggest that the free energy barrier increases with increasing polarity of the solvent, and that the solvent effects are stronger for the PCET TS than the stacking HAT TS pathway. The reason for this is discussed based on the dipole moment of different TS structures in solution. Copyright for JCC Journal: © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011