The role of bridged structures in the mechanism of the reaction between chlorine atom and ethylene

Braña, Pedro; Menéndez, Bibiana; Fernández, T.; Sordo, José

doi:10.1016/s0009-2614(00)00727-2

Cited by 9 publications

(16 citation statements)

References 16 publications

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“…These levels of theory were chosen bearing in mind the results of previous studies on similar systems. 15,16,19 The structures located on the PESs were characterized as minima or transition structures by computing the corresponding Hessian matrices. Graphical analysis of the imaginary frequency associated with the transition structures and intrinsic reaction coordinate (IRC) 25,26 calculations provided the required topological information to interconnect all the structures.…”

Section: Methodsmentioning

confidence: 99%

“…According to our previous experience, 15,16,19 we improved the energetics by performing QCISD(T)/aug-cc-pVDZ//MP2/aug-ccpVDZ calculations. The MP2/aug-cc-pVDZ geometries were preferred to the MP2/6-31G(d,p) ones used previously 16,19 because in the present case the Dunning augmented basis set leads to a more uniform mechanistic picture for the abstraction process (see below).…”

Section: Methodsmentioning

confidence: 99%

“…After surmounting almost negligible barriers (TSA add , TSB add ), the two radicals CH 3 45 It should be stressed at this point that the presence of I add and TS add on the (⌬U) PES [confirmed in similar reactions by using high levels of theory involving QCISD(T) optimizations] 16 is important from a mechanistic viewpoint to explain the stereochemical control exercised in reactions involving haloalkyl radicals. 15,16 Taking into account that the TSA add barrier is negligible, there will be no accumulation of I add . The application of the steady-state approximation to C 3 H 6 .…”

Section: Addition Reactionmentioning

confidence: 99%

“…Some important consequences arising from the presence of weakly bound complexes on the potential energy surfaces (PESs) for these reactions have been reported in recent studies. 15,16 Intermediate van der Waals complexes have been shown to become specially relevant for systems with significant tunneling effects 17 or in the cases where negative Arrhenius activation energy parameters are observed. 18 It has also been shown that the existence of intermediate complexes on the PES allows one to rationalize the pressure dependence experimentally observed in the abstraction reaction between chlorine atoms and isoprene.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

Braña

Sordo

2003

J Comput Chem

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The potential energy surface for the Cl + propene reaction was analyzed at the MP2 level using Pople's 6-31G(d,p) and 6-311+G(d,p), and Dunning's cc-pVDZ and aug-cc-pVDZ basis sets. Two different channels for the addition reaction leading to chloroalkyl radicals and five alternative channels for the abstraction reaction leading to C(3)H(5) (.) + HCl were explored. The corresponding energy profiles were computed at the QCISD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ level of theory. Theoretical results suggest that the previously established mechanism consisting of (1) direct abstraction and (2) addition-elimination steps is instead made up of (1) addition through an intermediate and (2) two-step abstraction processes. No direct abstraction mechanism exists on the potential energy surface. The kinetic equations derived for the new mechanism are consistent with the pressure dependence experimentally observed for this reaction.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Addition Reactionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

Braña

Sordo

2003

J Comput Chem

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“…Some preliminary results [MP2/6-31G(d,p) and QCI/6-31G(d,p) results in Table 2] have been reported elsewhere. 50 Therefore, only a brief comment on the mechanistic aspects emerging from Figure 2, emphasizing the new results obtained, is presented here. Figure 2 shows a simplified qualitative scheme representing the addition channel arising from the MP2 and QCISD calculations [QCISD(T)/6-31G(d,p) and QCISD(T)/cc-pVDZ optimizations were also carried out for Iadd and TSadd; see below] and Figure 3 , the corresponding one from DFT (Becke3LYP) calculations.…”

Section: Table 1: Most Significant Geometrical Parameters As Computedmentioning

confidence: 99%

Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

et al. 2000

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The potential energy surface of the reaction between chlorine atom and ethylene was explored at the MP2/ 6-31G(d,p), Becke3LYP/6-31G(d,p), QCISD/6-31G(d,p), MP2/6-311+G(d,p), MP2/6-311++G(3df,3pd), and MP2/aug-cc-pVDZ levels of theory. Further QCISD(T)/6-31G(d,p) and QCISD(T)/cc-pVDZ optimizations were performed for some structures of special interest. The geometrical parameters computed for the different structures located on the potential energy surface do not differ too much when employing different methods and basis sets with the only exceptions of those structures involving long distance interactions (van der Waals structures). The pronounced flatness of the potential energy surface in the regions where these structures appear seems to be the responsible for the observed discrepancies. The full optimized QCISD structures tend to become less stable than those computed at the MP2 level, whereas the opposite is true for the Becke3LYP structures. At the MP2 and QCISD levels, the transition structure associated with a direct shuttle motion in the addition channel is too high in energy to be involved in the dissociation mechanism. The existence of two bridged structures Iadd (minimum) and TSadd (transition structure) on the potential energy surface helps to explain the experimentally detected stereochemical control exercised by the chlorine atom in reactions involving haloethyl radicals. Contrarily, the Becke3LYP calculations suggest a mechanism in which the direct shuttle motion could play a relevant role, although the competing mechanism of rotation around the C-C bond is lower in energy. The MP2 and QCISD abstraction channels also differ considerably from the Becke3LYP one. However, in this case all the different potential energy surfaces seem to be consistent with the reported experimental data on the activation energy and endothermicity for the abstraction reaction. The QCISD(T)/ aug-cc-pVDZ//QCISD/6-31G(d,p) relative energies and barrier heights are consistent with the experimental data available on exo/endothermicities and activation barriers for the addition and abstraction reactions.

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A theoretical study on the mechanism of the reaction between Cl atoms and nitrobenzene

Praña

Gomperts

Sordo

2004

Chemical Physics Letters

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The role of bridged structures in the mechanism of the reaction between chlorine atom and ethylene

Cited by 9 publications

References 16 publications

Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction

Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

A theoretical study on the mechanism of the reaction between Cl atoms and nitrobenzene

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