Energetics and electronics of polar Diels–Alder reactions at the atomic level: QTAIM and IQA analyses of complete IRC paths

Atoms in molecules in real space: a fertile field for chemical bonding

“…Within this context, the IQA method can provide much valuable information, not only by assessing the energetic magnitude and essential features of chemical contacts in diverse scenarios, but also by providing quantitative descriptors of those concepts that are not associated with Dirac observables and thereby lack a rigorous mathematical definition. Thus, we will show that the applicability of the QTAIM and IQA methods is gradually expanding and, as recently noticed by Richter et al , 126 their additional computational effort is more than compensated by the great amount of useful information they provide. Several authors have used IQA to provide unified models of chemical bonding.…”

“…156 On the other hand, the geometric and electronic deformation of a diene/dienophile helps to understand the origin of the endo–exo preference in prototypical Diels–Alder reactions 157 while the atomic IQA decomposition of the IRC profiles explains the synchronous or asynchronous character of the polar Diels–Alder reactions. 126 Focusing also on the proper fragment quantities, the IQA study of the bifunctional catalysis played by water clusters 158 shows how water monomers encompassing the reaction between SO 3 and H 2 O to yield H 2 SO 4 mitigate the changes in chemical bonding across the rate-limiting step of the process, thereby reducing the activation energy as more water molecules are included in the system. Similar results are obtained for the hydrolysis of oxyrane and its methyl derivatives in neutral water.…”

The increased Diels–Alder reactivity of umpolung tropone: analysis of individual atoms and bonds using QTAIM and IQA along complete IRC paths

“…This methodology was implemented and fully automatized recently. 13 Even though the IQA@IRC protocol might seem challenging, considering the computational cost needed, the results it yields more than compensate the computation effort employed in the analysis, 14 as can be seen from the increasing number of studies reporting various kinds of IQA-based analysis applied to reactivity mechanisms. [15][16][17][18][19] F I G U R E 1 Scheme for the Diels-Alder (DA) reactions studied in this work, featuring maleimide (M) as the dienophile and the five different dienes: tropone (1) and the umpolung derivatives 2prot, 2, 3prot, and 3.…”

“…Therefore, the IQA@IRC analysis decomposes the energy pathway of the standard IRC calculation in individual energy terms for all atoms in the molecule, allowing us to access information about what atoms are the main responsible for the high/low energy value at a given (any) point along the IRC. This methodology was implemented and fully automatized recently 13 . Even though the IQA@IRC protocol might seem challenging, considering the computational cost needed, the results it yields more than compensate the computation effort employed in the analysis, 14 as can be seen from the increasing number of studies reporting various kinds of IQA‐based analysis applied to reactivity mechanisms 15–19 …”