The Third Dimension of a More O'Ferrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)(2)H(•) with X = O, NH, and CH(2).
The Third Dimension of a More O'Ferrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)(2)H(•) with X = O, NH, and CH(2).
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DOI：
10.1021/ct3004595
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发表时间：
2012-11-13
影响因子：
5.5
通讯作者：
Gao, Jiali
中科院分区：
文献类型：
--
作者：
Cembran, Alessandro;Provorse, Makenzie R.;Wang, Changwei;Wu, Wei;Gao, Jiali
质子耦合电子转移(PCET)反应包括氢原子转移(HAT)的理论表征中的一个关键因素是电子和质子局域非绝热状态的公式，在此基础上可以描绘出更多的O‘Ferrall-Jencks图来确定反应的阶梯性和协同性。虽然更多的O‘Ferrall-Jencks非绝热态常被用来建立PCET反应的理论模型，但这些态的势能面从来没有基于电子结构理论的第一性原理计算而被直接确定。这是由于在波函数或密度泛函理论计算中缺乏约束电子和质子局域非绝热态的实用方法。采用多态密度泛函理论(MSDFT)，其中电子和质子的定域非绝热组态是通过Kohn-Sham轨道的块定域化构造的，我们证明了协同质子-电子转移(CPET)和HAT之间的区别，这是通过考察包括基态和激发态势表面的更多O‘Ferrall-Jencks图的第三维来区分的。此外，我们还建立了一对有效的两态价键模型来描述CPET和HAT机制。我们发现，CPET和HAT有效非绝热态在交点的较低能量可以作为区分这两种机制的能量判据。在(PhX)2H·中氢交换反应的等电子系列中，X=O、NH和CH2时，苯氧基-苯酚对的CPET反应机理向苯基和甲苯的HAT反应连续转变，而PhNH2和PhNH·的反应具有CPET和HAT反应的中间机理.苯酚体系中CPET机理的电子非绝热性质可归因于基态表面和激发态表面之间的重叠相互作用，导致绝热基面和激发态势能面上近似正交的最小能量路径。另一方面，HAT机制的绝热基态上的最小能量路径与激发态上的最小能量路径重合，产生了一个大的电子耦合，使两个表面之间的距离超过120kcal/mol。
A critical element in theoretical characterization of the mechanism of proton-coupled electron transfer (PCET) reactions, including hydrogen atom transfer (HAT), is the formulation of the electron and proton localized diabatic states, based on which a More O’Ferrall-Jencks diagram can be represented to determine the step-wise and concerted nature of the reaction. Although the More O’Ferrall-Jencks diabatic states have often been used empirically to develop theoretical models for PCET reactions, the potential energy surfaces for these states have never been determined directly based on first principles calculations using electronic structure theory. The difficulty is due to a lack of practical method to constrain electron and proton localized diabatic states in wave function or density functional theory calculations. Employing a multistate density functional theory (MSDFT), in which the electron and proton localized diabatic configurations are constructed through block-localization of Kohn-Sham orbitals, we show that distinction between concerted proton-electron transfer (CPET) and HAT, which are not distinguishable experimentally from phenomenological kinetic data, can be made by examining the third dimension of a More O’Ferrall-Jencks diagram that includes both the ground and excited state potential surfaces. In addition, we formulate a pair of effective two-state valence bond models to represent the CPET and HAT mechanisms. We found that the lower energy of the CPET and HAT effective diabatic states at the intersection point can be used as an energetic criterion to distinguish the two mechanisms. In the isoelectronic series of hydrogen exchange reaction in (PhX)2H•, where X = O, NH, and CH2, there is a continuous transition from a CPET mechanism for the phenoxy radical-phenol pair to a HAT process for benzyl radical and toluene, while the reaction between PhNH2 and PhNH• has a mechanism intermediate of CPET and HAT. The electronically nonadiabatic nature of the CPET mechanism in the phenol system can be attributed to the overlap interactions between the ground and excited state surfaces, resulting in roughly orthogonal minimum energy paths on the adiabatic ground and excited state potential energy surfaces. On the other hand, the minimum energy path on the adiabatic ground state for the HAT mechanism coincides with that on the excited state, producing a large electronic coupling that separates the two surfaces by more than 120 kcal/mol.
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影响因子：
18.3
作者：
Hammes-Schiffer, Sharon
通讯作者：
Hammes-Schiffer, Sharon
影响因子：
--
作者：
Cukier, RI
通讯作者：
Cukier, RI
影响因子：
3.3
作者：
Cukier, RI
通讯作者：
Cukier, RI
影响因子：
4.4
作者：
BECKE, AD
通讯作者：
BECKE, AD
影响因子：
62.1
作者：
Hammes-Schiffer, Sharon;Stuchebrukhov, Alexei A.
通讯作者：
Stuchebrukhov, Alexei A.