Hidden intermediate activation: a concept to elucidate the reaction mechanism of the Schmittel cyclization of enyne–allenes

Abstract

The mechanistic paradigm in which the Schmittel cyclization transit from one-step to stepwise has been investigated through the stabilization of a full hidden intermediate in the framework of the Diabatic...

Reaction mechanism – explored with the unified reaction valley approach

“…139 It is interesting to note that these full hidden intermediates are only reachable through molecular dynamics or ‘hot’ trajectories. 140,141 As revealed by Fig. 3 each curvature peak is flanked by two curvature minima.…”

CO2 Capture by Diamines in Dry and Humid Conditions: A Theoretical Approach

“…Interestingly, it was not possible to optimize the geometry of the zwitterion because it did not have the characteristics of a stationary point on the potential energy surface, corresponding to a reaction intermediate. Hence, this transient structure is a hidden intermediate. , As described elsewhere, the RIRC technique allows to precisely locate all meaningful entities in the potential energy surface, including any hidden intermediate or quasi-transition state. Figure a shows the location of the zwitterion (Z) corresponding to the hidden intermediate and the quasi-transition state TS′, leading to the formation of carbamic acid.…”

“…The curvatures of the force profile provide key information regarding the reaction mechanism . As a reminder, in a concerted mechanism, there are two convex curves corresponding to the approach phase of the reactants and the release of the product(s), whereas a two-step mechanism consists of two consecutive concerted mechanisms, where the products of the first step are the reactants of the second, allowing the localization of a reaction intermediate. , The concerted asynchronous mechanism is intermediate between the concerted and the two-step mechanisms. In the corresponding force profile, the superposition of the curves describing the end of the first process, and the beginning of the second process gives rise to a new maximum, which does not correspond to a stationary point.…”

“…50 As a reminder, in a concerted mechanism, there are two convex curves corresponding to the approach phase of the reactants and the release of the product(s), whereas a two-step mechanism consists of two consecutive concerted mechanisms, where the products of the first step are the reactants of the second, allowing the localization of a reaction intermediate. 49,50 The concerted asynchronous mechanism is intermediate between the concerted and the two-step mechanisms.…”

“…Hence, this transient structure is a hidden intermediate. 48,49 As described elsewhere, 40 the RIRC technique allows to precisely locate all meaningful entities in the potential energy surface, including any hidden intermediate or quasi-transition state. Figure 2a shows the location of the zwitterion (Z) corresponding to the hidden intermediate and the quasi-transition state TS′, leading to the formation of carbamic acid.…”