Valence bond representation for the hydrogen atom exchange reaction

Harcourt, Richard D.; Ng, Rickie

doi:10.1021/j100149a019

Cited by 17 publications

(32 citation statements)

References 5 publications

(5 reference statements)

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“…[21] Although this challenge may seem unimpressive in comparison with the current capabilities of MO-based methods, this is not the case for VB theory. Thus, an earlier VB study by Harcourt and Ng, [34] used the STO-6G basis set, and arrived at a barrier of 23.6 kcal mol…”

Section: Hàh Hmentioning

confidence: 99%

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

Song

Hiberty

et al. 2003

Chemistry A European J

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One of the landmark achievements of quantum chemistry, specifically of MO-based methods that include electron correlation, was the precise calculation of the barrier for the hydrogen-exchange reaction (B. Liu, J. Chem. Phys. 1973, 58, 1925; P. Siegbahn, B. Liu, J. Chem. Phys. 1978, 68, 2457). This paper reports an accurate calculation of this barrier by two recently developed VB methods that use only the eight classical VB structures. To our knowledge, the present work is the first accurate ab initio VB barrier that matches an experimental value. Along with the accurate barrier, the VB method provides accurate bond energies and diabatic quantities that enable the barrier height to be analyzed by the VB state correlation diagram approach, VBSCD (S. Shaik, A. Shurki, Angew. Chem. 1999, 111, 616; Angew. Chem. Int. Ed. Engl. 1999, 38, 586). This is a proof of principal that VB theory with appropriate account of dynamic electron correlation can achieve quantitative accuracy of reaction barriers, and still retain a compact and interpretable wave function. A sample of S(N)2 barriers and dihalogen bonding energies, which are close to CCSD(T) and G2(+) values, show that the H(3) problem is not an isolated case, and while it is premature to conclude that VB theory has come of age, the occurrence of this event is clearly within sight.

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Section: Hàh Hmentioning

confidence: 99%

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

Song

Hiberty

et al. 2003

Chemistry A European J

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“…When Ψ II ) Φ′ II and Ψ III ) Φ′ III , the polarity parameters l and λ for VII and VIII have nonzero values when they are determined variationally. 5 But the resultant wave functions for VII and VIII are then not orthogonal to the ground-state wave functions for the separated products or reactants, 5 and therefore they do not correspond to spectroscopic (excited) states.…”

Section: The Promotion Gap Gmentioning

confidence: 99%

“…We shall initially designate these structures as Φ 1 instead of Φ HL (r; 1 ) or Φ HL (p; 1 ) for example. The Φ‘ II , Φ‘ ‘ II , Φ‘ III , and Φ‘ ‘ III wave functions of eqs 5−8 of ref are then given by eqs 3−6 here: in which a = 1 + k ‘ k ‘ ‘, b = 1 − k ‘ k ‘ ‘, u = 1 + κ‘κ‘ ‘, and v = 1 − κ‘κ‘ ‘.…”

Section: Wave Functions For Vb Structuresmentioning

confidence: 99%

“…After the publication of ref , Shaik et al contrasted their model with the Z model of Zavitsas, to respond to a criticism that was provided by Zavitsas . In ref , a different type of quantitative VB study for H • + H−H‘ → H−H + H‘ • was also presented. Although ref involved an extensive list of corrections, the treatment provided is relevant for the provision of compact qualitative VB representations for X • + H−X‘ → X−H + X‘ • radical transfer reactions.…”

Section: Introductionmentioning

confidence: 99%

“…In ref , a different type of quantitative VB study for H • + H−H‘ → H−H + H‘ • was also presented. Although ref involved an extensive list of corrections, the treatment provided is relevant for the provision of compact qualitative VB representations for X • + H−X‘ → X−H + X‘ • radical transfer reactions. In particular, Scheme A of ref , or more generally I → [ II ↔ III ] → IV here 6 with X = R = Y = H, does indicate clearly how reactants are converted into products via the formation of reactantlike (RC) and productlike (PC) complexes.…”

Section: Introductionmentioning

confidence: 99%

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Valence Bond Formulations of the Identity Hydrogen Abstraction Reaction, X^• + H−X‘ → X−H + X‘^•, with Reactantlike and Productlike Complexes

Harcourt

2003

J. Phys. Chem. A

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Connections are made between two valence bond studies of hydrogen atom abstraction reactions: (a) J. Phys. Chem. A 2001, 105, 8226 and (b) J. Phys. Chem. 1993, 97, 12210; corrections 1994, 98, 3226. At each stage along the reaction coordinate, the variational-best valence bond formulation for the reacting system of (b) can be described in terms of resonance between valence bond structures for a reactantlike complex and a productlike complex. It is demonstrated that the (a) and (b) descriptions of the transition states are equivalent. Further development for (b) is presented, to compare expressions for the promotion gap (G) and the resonance energy at the avoided crossing (B) with those that arise in (a). By use of a triple-ζ 1s atomic orbital (AO) basis set to formulate the wave functions for the reactantlike and productlike complexes, it is demonstrated how these wave functions are constructed as linear combinations of localized molecular orbital (MO) configurations, each of which involves one AO per atomic center. Similar procedures that include 2p AOs as polarization functions in the treatment are also described. The results of valence bond calculations that use these two types of AO basis sets provide illustrative examples of how the formulation of (b) provides a compact valence bond representation for the electronic reorganization that is involved in the conversion of reactants into products.

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Increased-valence structures and hypervalent molecules

Harcourt

1996

Int. J. Quantum Chem.

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rnHypervalent molecules may involve the use of increased-valence structures to provide valence bond descriptions of their electronic structure. For electron-rich molecules with four electrons distributed among three overlapping (nuclear-centered) atomic orbitals, the increased-valence structures are Y-A * B and ? -A--B. Each structure involves a fractional electron-pair bond and a one-electron bond. It is deduced that the Armstrong-Perkins-Stewart valence of the A atom is able to exceed unity in each of these structures when the three bonding electrons occupy nonorthogonal localized molecular orbitals. It is also shown that increased valence for the A atom does not occur when the four electrons occupy localized molecular orbitals to give the valence-bond structure Y-A-B with three overlapping atomic orbitals, and the same number of orbital variational parameters as occurs in the wave functions for either of the increasedvalence structures. The results of ab initio valence bond calculations with minimal basis sets are reported for HT1, CH;, HF,, F,, CIF,, and FF,, and the resulting wave functions for resonance between six canonical Lewis structures are related to those for resonance between the two increased-valence structures. The use of the latter structures to indicate how electronic reorganization proceeds via one-electron delocalizations for S,Z reactions is redescribed, and an elementary argument is presented to deduce that this class of reactions cannot involve the delocalization of a pair of electrons in concert from the nucleophile. Increased-valence wave functions are used to deduce an expression for the avoided crossing for the transition state of the identity S , Z reaction.

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Valence bond representation for the hydrogen atom exchange reaction

Cited by 17 publications

References 5 publications

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

Valence Bond Formulations of the Identity Hydrogen Abstraction Reaction, X^• + H−X‘ → X−H + X‘^•, with Reactantlike and Productlike Complexes

Increased-valence structures and hypervalent molecules

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Valence bond representation for the hydrogen atom exchange reaction

Cited by 17 publications

References 5 publications

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

An Accurate Barrier for the Hydrogen Exchange Reaction from Valence Bond Theory: Is this Theory Coming of Age?

Valence Bond Formulations of the Identity Hydrogen Abstraction Reaction, X• + H−X‘ → X−H + X‘•, with Reactantlike and Productlike Complexes

Increased-valence structures and hypervalent molecules

Contact Info

Product

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Valence Bond Formulations of the Identity Hydrogen Abstraction Reaction, X^• + H−X‘ → X−H + X‘^•, with Reactantlike and Productlike Complexes