The behavior of quantum chemical bond order in the vicinity of a saddle point on the reaction path

Maity, Dilip Kumar; Bhattacharyya, S. P.

doi:10.1021/ja00164a060

Cited by 28 publications

(15 citation statements)

References 4 publications

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“…Maity et al − claimed that the transition state would be located at the inflection point of the forming and breaking bond order curves. Table showed our results considering data from −0.8 to 0.8 on the reaction coordinate, with the transition state lying at 0.0.…”

Section: Discussionmentioning

confidence: 99%

“…The bond order as defined by Pauling 4 was used; where n is the bond order at some bond length, R , compared to an equilibrium bond length, R eq . The constant, a , has been reported to have values ranging from 0.2 to 0.4, with 0.26 most frequently used. − While others have argued that a should vary with R eq , a value of 0.3 was chosen for this work. Values of a larger than 0.3 moved the transition states later, while smaller values moved the transition state earlier.…”

Section: Methodsmentioning

confidence: 99%

“…As ab initio calculations have become cheaper through code and computer architecture improvements, the validity of bond order conservation has been investigated. So far, gas-phase three-center linear reactions, − gas-phase isomerizations, − small group transfer reactions in the gas phase, − and pericyclic reactions have been studied. Also, its validity has been verified for diatomic dissociation on some metal surfaces …”

Section: Introductionmentioning

confidence: 99%

“…The forming and breaking bond order curves have been used to predict the location of the transition state. The transition state has previously been located at the inflection point of the forming and breaking bond order curves [25][26][27] for three-center isomerization reactions. On the other hand, the transition state has also been found to lie at the minimum of the total bond order curve for polyatomic atom reactions.…”

Section: Introductionmentioning

confidence: 99%

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Conservation of Bond Order during Radical Substitution Reactions: Implications for the BEBO Model

Blowers

Masel

1998

J. Phys. Chem. A

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The bond energy−bond order model has been used extensively to predict behaviors and energetics of species where ab initio calculations are still too expensive. However, the accuracy of bond order conservation, even for small polyatomic systems, is still unknown. In this paper, we use ab initio calculations at the PMP2 = (full)/6-31 g* and G-2 level to examine bond order conservation for the following gas-phase radical substitution reactions: H* + CH3OH → CH3H* + OH, H* + CH3OH → HOH* + CH3, H* + CH3OH → HH* + CH2OH, H* + CH3OH → HH* + CH3O, H* + CH3OH → H + CH2H*OH, H* + CH3OH → H + CH3OH*. We find that total bond order is approximately conserved during atom transfer reactions, but is not conserved during the more complicated hydrogenolysis reactions or during hydrogen exchange on oxygen. An early transition state is predicted for hydrogen exchange on oxygen, and late ones for the hydrogenolysis reactions. Even though the transition state structures may differ greatly from the ab initio predictions, the barrier heights predicted with bond order conservation are only incorrect by 1−2 kcal/mol. This behavior arises because the potential energy surfaces are relatively flat in the region where the transition states are found. Consequently, the energies of the transition state predicted with either method are in close agreement, even though the structures are poorly represented by bond order conservation methods.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Conservation of Bond Order during Radical Substitution Reactions: Implications for the BEBO Model

Blowers

Masel

1998

J. Phys. Chem. A

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“…Also, in some unsymmetrical atom-transfer reactions the inflection point in the bond order profile does not coincide with the saddle point in the corresponding energy plot. 47 Recent ab initio studies showed that electronegativity differences between the end atoms in Scheme 1 lead to polar transition states, l6 and the resulting charge separation was claimed to be the source of enhanced 01 values. Shi and Boyd4* reinforced this interpretation and added that the electronic structure of the TS is another factor influencing its charge development.…”

Section: (7)mentioning

confidence: 99%

Towards a general approach to the deprotonation of carbon acids, including nitroalkanes

Arnaut

1991

J of Physical Organic Chem

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The deprotonation of nitroalkanes and ketones was studied through the intersecting state model of Formosinho. The anomalous Brønsted coefficients observed when substituted nitroalkanes react with a common base are explained in terms of variable transition‐state electronic structures. These are very sensitive to substitution in the nitroalkane, owing to the high electron affinity of the nitro group. In ketones, such electronic effects are much attenuated. The transition states are characterized by the bond order, n,*, which is quantitatively correlated to the field/inductive and resonance effects of the substituents. The deprotonation of fluorence and other carbon acids was also studied. The theoretical model applied shows that all these reactions follow a mechanistic continuum, dictated by the extent into which the group directly bonded to the acidic carbon is mixed in the reaction coordinate.

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Natural resonance theory: II. Natural bond order and valency

1998

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The behavior of quantum chemical bond order in the vicinity of a saddle point on the reaction path

Cited by 28 publications

References 4 publications

Conservation of Bond Order during Radical Substitution Reactions: Implications for the BEBO Model

Conservation of Bond Order during Radical Substitution Reactions: Implications for the BEBO Model

Towards a general approach to the deprotonation of carbon acids, including nitroalkanes

Natural resonance theory: II. Natural bond order and valency

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