Chemical reaction with two different elementary transition states

Abstract

The phenomenon of the elementary chemical reaction with two different transition states (TSs) between reactant and product is represented. Different examples of the reaction with two transition states were reported during the last decade. In some cases, one route is dominant, in another cases the energy of the barriers is similar, but the electronic structure of TSs are different. The Valence Bond (VB) approach provides the rationalization for the phenomenon of the chemical reaction with two TSs: the reactant and product pair is based on three dominant VB structures (anchors). The VB approach provides an opportunity to distinguish between different resonance mechanisms -different TSs. The 2D-domain is based on two minima, the reactant and the product, which are connected by two different TSs and can include the electronic degeneracy. Physical consequences of the chemical reaction with dual reaction routes are discussed.

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“…Cis‐trans isomerization around polar double bond is a well‐documented example of the chemical reaction with two TSs. One TS is a biradical covalent form without polar contribution, whereas the second TS has a dominant polar contribution and can be defined as zwitterion . This kind of dual reaction routes was discovered for different molecules with C=C polar bond …”

“…One TS is a biradical covalent form without polar contribution, whereas the second TS has a dominant polar contribution and can be defined as zwitterion. [13] This kind of dual reaction routes was discovered for different molecules with C=C polar bond. [14,15] Conical intersection (CI) escorted by two isomeric TSs was reported for the different cis-trans photoisomerization reactions.…”

“…However, the splitting of the covalent‐polar pair to the pure covalent or zwitterionic structures is possible. Consider VB presentation of the cis‐trans isomerization around the polar double bond:…”

“…However, the splitting of the covalent-polar pair to the pure covalent or zwitterionic structures is possible. Consider VB presentation of the cis-trans isomerization around the polar double bond: [13] Two isomers -reactant and product have a common polar (zwitterionic) form (Zw) and two different covalent forms (C 1 and C 2 ). 1) The ground state reaction is going through a TS which described by an anti-combination wave function jΨ À > if covalent contribution (C 1 /C 2 ) is dominant.…”

“…Two routes are possible in the ground state in the case of transformation between two isomers with the similar contribution of polar and covalent forms (Scheme 2). [13] This is a chemical reaction with single product, two different TSs and a conical intersection inside the closed loop (Figure 2). Different examples of cis-trans isomerization reaction with two reaction routes were documented.…”