Proton transfer in phenol-amine complexes: phenol electronic effects on free energy profile in solution.
Free energy profiles for the proton transfer reactions in hydrogen-bonded complex of phenol with trimethylamine in methyl chloride solvent are studied with the reference interaction site model self-consistent field method. The reactions in both the electronic ground and excited states are considered. The second-order Møller-Plesset perturbation (MP) theory or the second-order multireference MP theory is used to evaluate the effect of the dynamical electron correlation on the free energy profiles. The free energy surface in the ground state shows a discrepancy with the experimental results for the related hydrogen-bonded complexes. To resolve this discrepancy, the effects of chloro-substitutions in phenol are examined, and its importance in stabilizing the ionic form is discussed. The temperature effect is also studied. In contrast to the ground state, the ππ* excited state of phenol-trimethylamine complex exhibits the proton transfer reaction with a low barrier. The reaction is almost thermoneutral. This is attributed to the reduction of proton affinity of phenol by the ππ* electronic excitation. We further examine the possibility of the electron-proton-coupled transfer in the ππ* state through the surface crossing with the charge transfer type πσ* state.
Aono
Shinji
S
Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan. saono@icems.kyoto-u.ac.jp
Kato
Shigeki
S
D004583:Electrons; D006860:Hydrogen Bonding; D008737:Methyl Chloride / Q000737:chemistry; D008744:Methylamines / Q000737:chemistry*; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D012996:Solutions; D013499:Surface Properties; D013696:Temperature; D013816:Thermodynamics
D008744:Methylamines; D010636:Phenols; D011522:Protons; D012996:Solutions; D008737:Methyl Chloride; C023336:trimethylamine