Orbital symmetry, orbital stability, and orbital pairing rules for organic reactions in the ground state

Yamaguchi, Kizashi

doi:10.1002/qua.560220303

Cited by 17 publications

(5 citation statements)

References 77 publications

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“…Configuration correlation diagrams are also derived on the basis of the BS MO correlation schemes. Thus, basic notions of magnetism and chemical bonds play important roles for derivations of spin alignments rule in material science 52 and spin pairings rule in chemical reaction 53: both are main topics in theory of molecular magnetism 54. Collective motions, superparamagnetism and radical reactivity in mesoscopic systems such as Au clusters 55–63 will be discussed in relation to true spin symmetry breaking in chemical reactions elsewhere (see Supporting Information).…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Extended Hartree–Fock theory of chemical reactions. IX. Diradical and perepoxide mechanisms for oxygenations of ethylene with molecular oxygen and iron‐oxo species are revisited

Yamaguchi¹,

Yamanaka²,

Shimada³

et al. 2009

Int J of Quantum Chemistry

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Symmetry and broken symmetry (BS) in molecular orbital description of transition structures and intermediates in oxygenation reactions have been revisited to elucidate states correlation diagrams and mechanisms for addition reactions of molecular oxygen and metal-oxo MAO (M ϭ Mn(II) and Fe(II)) species to CAC double bonds. Relative stabilities between diradical (DR) and perepoxide (PE) intermediates were thoroughly investigated by several BS hybrid DFT (HDFT) methods and BS CCSD(T) method with and without spin projection. It has been found that recovery of spin symmetry, namely eliminating spin contamination error from the BS solutions, is crucial for the elucidation of reasonable state correlation diagrams and energy differences of the key structures in the oxygenation reactions because the singlet-triplet energy gap for molecular oxygen is large (22 kcal/mol). The BS HDFT followed by spin correction reproduced activation barriers for transition structures along both PE and DR reaction pathways by the use of the CASPT2 method. Basis set dependence on the relative stability between PE and DR intermediates were also examined thoroughly. Solvation effect for DR and PE intermediates was further examined with self-consistent reaction field (SCRF) and SCIPCM methods. Both BS HDFT and CASPT2 have concluded that the DR mechanism is favorable for the addition reaction of singlet oxygen to ethylene, supporting our previous conclusions. The BS HDFT with spin correction was concluded to be useful enough for theoretical investigations of mechanisms of oxygenation reactions. Implications of the computational results were discussed in relation to the theoretical framework (four configuration model) for elucidation of possible mechanisms of epoxidation reactions with Fe(IV)AO cores in metalloenzymes on the basis of isolobal analogies among O, OAO, and Fe(IV)AO. Correspondence between magnetic coupling mode and radical pathway in oxygenations with these species was clarified based on the BS MO interaction diagrams, leading to local singlet and triplet diradical mechanisms for epoxidations.

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Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Extended Hartree–Fock theory of chemical reactions. IX. Diradical and perepoxide mechanisms for oxygenations of ethylene with molecular oxygen and iron‐oxo species are revisited

Yamaguchi¹,

Yamanaka²,

Shimada³

et al. 2009

Int J of Quantum Chemistry

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“…For normal closed-shell molecules, the singlet triplet energy difference Δ E ST is related to the energy of a HOMO−LUMO excitation (i.e., it is on the order of several electron volts), whereas diradicals feature very small values of Δ E ST …”

Section: Cleavage Mechanismsmentioning

confidence: 99%

A Quantum Chemical Study of Photoinduced DNA Repair: On the Splitting of Pyrimidine Model Dimers Initiated by Electron Transfer

1996

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As a first step toward modeling the photoinduced repair of DNA, electronic structure calculations on the cleavage reaction of various pyrimidine dimers (uracil, thymine, and cytosine) as well as of their anion and cation radicals have been carried out using the AM1 UHF method. Two different paths of the splitting reaction have been studied by locating all stationary points. Along the first path, the opening of the cyclobutane ring is initiated by breaking the C5−C5‘ bond which leads to the formation of an intermediate, followed by the cleavage of the C6−C6‘ bond; along the second path, the two C−C‘ bonds are broken in reverse order. The results for the dimer anion radical favor a cleavage reaction along the first path while the second path is preferred for the cation radicals. Electron transfer to the dimers does not appreciably influence the enthalpy of the reaction for cycloreversion in the uracil and thymine dimers; however, it causes a dramatic reduction of the activation barrier for the cleavage reaction. In contrast, the reactivity of the cytosine dimer is only weakly affected by this electron uptake. Differences in the various reaction profiles are rationalized by invoking an energetic stabilization associated with the charge delocalization between fragments in the corresponding transition states. The calculated solvent effects evaluated by a dielectric continuum model show that the splitting reaction is sensitive to a polar environment. The reaction barriers of the splitting reaction are found to increase with the polarity of the medium, rationalizing the experimentally observed solvent effects on the dimer cleavage.

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“…The hole popula-t = Tl(T)/Tl(U) = Tl(UT)/Tl(U). The excitation energies for the M06 cluster were calculated for three cases; (1) the conditions a and b, (2) the conditions a and c , (3) the conditions a and d . Table I1 summarizes the calculated excitation energies.…”

Section: Hole Populations and Symmetries Of Holesmentioning

confidence: 99%

“…The symmetry and broken symmetry properties of molecular orbitals are elucidated by the symmetry and instability analysis of the Hartree-Fock solutions [2]. These properties are examined in relation to concerted and nonconcerted behaviors of organic reactions [3]. Recent ab initio instability analysis has indicated that the triplet instability often occurs for the closed-shell Hartree-Fock (HF) solutions of transition structures even for concerted reactions [4].…”

Section: Introductionmentioning

confidence: 99%

N‐band Hubbard models for copper oxides and isoelectronic systems. New models for organic and organometallic magnetic conductors and superconductors

Yamaguchi

1990

Int J of Quantum Chemistry

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138

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The electronic structures of undoped and doped copper oxides and other related oxides are investigated on the basis of the N-band Hubbard models. The Hubbard Hamiltonians for clusters of transition metal oxides are exactly diagonalized by the full valence-bond (VB) configuration interaction (CI) method in order to elucidate populations of doped holes, electronic excitation energies, etc. Possible mechanisms of the high-T, superconductivity for oxide superconductors are discussed on the basis of the calculated results, together with available experiments. The analysis of correlation and spin correlation effects on doped copper oxides indicates theoretical possibilities of new models for organic and organometallic magnetic conductors and superconductors. Organic and organometallic analogs to copper oxides are therefore proposed on the basis of these results.

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Orbital symmetry, orbital stability, and orbital pairing rules for organic reactions in the ground state

Cited by 17 publications

References 77 publications

Extended Hartree–Fock theory of chemical reactions. IX. Diradical and perepoxide mechanisms for oxygenations of ethylene with molecular oxygen and iron‐oxo species are revisited

Extended Hartree–Fock theory of chemical reactions. IX. Diradical and perepoxide mechanisms for oxygenations of ethylene with molecular oxygen and iron‐oxo species are revisited

A Quantum Chemical Study of Photoinduced DNA Repair: On the Splitting of Pyrimidine Model Dimers Initiated by Electron Transfer

N‐band Hubbard models for copper oxides and isoelectronic systems. New models for organic and organometallic magnetic conductors and superconductors

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