Journal
JOURNAL OF COMPUTATIONAL CHEMISTRY
Volume 32, Issue 14, Pages 3081-3091Publisher
WILEY
DOI: 10.1002/jcc.21892
Keywords
electronic structure; phenol-phenoxyl radical; Hartree-Fock exchange; proton-coupled electron transfer; hydrogen atom transfer; solvent effect
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Funding
- International Center for Integrated Research and Advanced Education in Material Science, Kyoto University
- Ministry of Education and Science
- Grants-in-Aid for Scientific Research [21350010] Funding Source: KAKEN
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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 PCETTS than the stacking HAT TS pathway. The reason for this is discussed based on the dipole moment of different TS structures in solution. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 3081-3091, 2011
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