The Bonding Nature of Some Simple Sigmatropic Transition States from the Topological Analysis of the Electron Localization Function

Abstract

It is shown that the topological analysis of the electron localization function (ELF), a measure of the local Pauli repulsion, is a useful tool to describe the bonding nature of transition structures of simple pericyclic processes. In this work, we have revisited the [1s,3a]hydrogen, [1a,3s]methyl, and [1a,3s]fluorine simple sigmatropic rearrangements in the allyl system. Results based on the integrated densities over the ELF basins and their related properties at the B3LYP/6-311++G(d,p) level of theory showed explicitly a delocalized structure for the antarafacial (Cs) hydrogen rearrangement, a two radical interaction for the methyl suprafacial (C2) migration, and a pair−ion interaction for the fluorine suprafacial (Cs) transfer. Results on these well-studied systems confirm the topological analysis of the ELF as a useful descriptor for the study of bonding structure of pericyclic transition states. In this context, the ELF analysis is shown to be a complementary value to the Woodward−Hoffmann rules, which provide an orbital symmetry basis of understanding.

The Mysticism of Pericyclic Reactions: A Contemporary Rationalisation of Organic Reactivity Based on Electron Density Analysis

“…It is worth mentioning that the V(C1,H6,C5) trisynaptic basin present in P4 ‐ 4 becomes two V(C1) and V(C5) monosynaptic basins, related to two C1 and C5 pseudoradical centres, and one V(H1) monosynaptic basin, related to a free hydrogen nucleus, at the MPWB1K/6‐31G(d) level (see Figure S3 in Supporting Information). Note that a similar non‐bonding pattern was found in the TS associated with the [1,3] sigmatropic rearrangement of propene ( 8 ) at the B3LYP/6‐311++G(d,p) level …”

“…Note that a similar non-bonding pattern was found in the TS associated with the [1,3] sigmatropic rearrangement of propene (8) at the B3LYP/6-311++G(d,p) level. [37]…”

“…After the implementation of these QC topological tools at the beginning of this century, most of the organic reactions classified as “pericyclic reactions” were studied by using different DFT computational methods . Very recently, the electron density delocalisation in the TSs associated with the five pseudocyclic reactions given in Scheme was topologically analysed by using QTAIM and ELF .…”

“…After the implementation of these QC topological tools at the beginning of this century, most of the organic reactions classified as "pericyclic reactions" were studied by using different DFT computational methods. [34][35][36][37][38] Very recently, the electron density delocalisation in the TSs associated with the five pseudocyclic reactions given in Scheme 2 was topologically analysed by using QTAIM [22] and ELF. [23] That study evidenced that in four of the five cases, at least one pair of atoms is unbound in the TS, thus precluding a possible cyclic conjugation, and consequently, any aromatic character, [26] such as was suggested in the last century.…”

The nature of bonding in pericyclic and pseudopericyclic transition states: Thermal chelotropic decarbonylations

“…14 Because we are more interested here in exploring the reaction mechanism topologies at pericyclic and pseudopericyclic transition structures, we have resorted to the ELF picture of bonding. Previous work on benchmark pericyclic reactions corresponding to the ͓1 s ,3 a ͔-hydrogen, ͓1 a ,3 s ͔-methyl, and ͓1 a ,3 s ͔-fluorine 16 sigmatropic shifts in the allyl system have emphasized the usefulness of the analysis of properties of the electron density, integrated over the ELF basins, to obtain a clear picture of electronic rearrangement which is complementary to the traditionally used Woodward-Hoffmann analysis. We present here the first results from an ongoing systematic study concerning the characterization of bonding at pericyclic and pseudopericyclic transition states using the ELF analysis.…”