A vector‐based representation of the chemical bond for predicting competitive and noncompetitive torquoselectivity of thermal ring‐opening reactions

Abstract

We present a new vector-based representation of the chemical bond referred to as the bondpath frame-work set B = {p, q, r}, where p, q, and r represent three paths with corresponding eigenvector-following paths with lengths H*, H, and the bond-path length from the quantum theory of atoms in molecules (QTAIM). We find that longer path lengths H of the ring-opening bonds predict the preference for the transition state inward (TSIC) or transition state outward (TSOC) of thermal ring opening reactions in agreement with experiment for all five reactions R1-R5. Competitiveness and noncompetitiveness have traditionally been considered using activation energies within transition state theory that is known to fail for thermal ring-opening reactions. Consequently, we find that the activation energy for R3 does not satisfactorily determine competitiveness or provide consistent agreement with experimental yields. We choose a selection of five competitive and noncompetitive reactions; methyl-cyclobutene (R1), ethyl-methylcyclobutene (R2), iso-propyl-methyl-cyclobutene (R3), ter-butyl-methyl-cyclobutene (R4), and phenyl-methyl-cyclobutene (R5). Therefore, in this investigation we provide a new criterion, within the QTAIM framework, to determine whether the reactions R1-R5 are competitive or noncompetitive. We that find R2, R3, and R5 are competitive and R1 and R4 are noncompetitive reactions in contrast to the results from the activation energies, calling into question the reliability of activation energies.

Discerning Torquoselectivity of Non-Competitive and Competitive Ring-Opening Reactions Using QTAIM and Stress Tensor

“…This degenerate and non-degenerate behavior in the metallicity ξ(r b ) suggests that in fact Reaction 1is a competitive reaction and Reaction 2 , Reaction 3 , and Reaction 4 are non-competitive reactions on the chemical basis of metallicity being a key factor in understanding the electronic reorganization of the ring-opening BCP along the reaction pathways. In addition, based on the transition state theory and previous researches outcomes, we obtain that for all four reactions, the transition state and maximum metallicity ξ(r b ) relevant to the ring-opening C2-C3/C2-C3 BCP s do not simultaneously occur 48 . Subsequently, the degeneracy results from other QTAIM measures such as ellipticity ε and the total local energy density H In the following, investigation the plots of variation of stress tensor polarizability P σ with the IRC demonstrate an apparent differentiation among all four reactions.…”

Discerning torquoselectivity in a series of cyclobutene ring‐opening reactions using quantum theory of atoms in molecules and stress tensor

“…In recent years, there have been several developmental studies on torquoselectivity [5,6] that are characterized by either the preference of the transition state outward conrotatory (TSOC) or the transition state inward conrotatory (TSIC) reaction pathway of the substituents in the electrocyclic ring-opening reactions [7,8]. Cyclobutenes undergo thermally allowed conrotatory electrocyclic ring opening to form Z-dienes or E-dienes by inward or outward twisting, respectively.…”

“…Ongoing investigations have revealed new insights into how to address the bottleneck in electrocyclic reactions utilizing frameworks from the electron localization function [17,20], electronic structure principles [21] to stress tensor and QTAIM [5,22]. Even though just QTAIM and stress tensor frameworks permitted to quantify and identify the reaction coordinate through directional parameters, albeit the later was bounded to use with reactions with fundamentally similar nuclear skeletons.…”

“…Recently a pair of competitive reactions without the use of orbital information or symmetry demonstrated torquoselectivity along the reaction pathways successfully but this research was limited to sets of TSOC/TSIC competitive reactions with very similar nuclear skeletons and it was required to be performed on all bond critical points (BCPs) in each structure [23]. In addition, within our previous investigation, we selected a series of five reactions with contrasting nuclear skeletons and activation energies to consider non-competitive/competitive reactions as well as discover a method to distinguish the torquoselectivity preferences that accommodate the directional character of the reaction pathways without the use of orbital information or symmetry [5].…”

“…The goal of this current investigation is to expand our previous research [5] for a new series of four thermal non-competitive/competitive electrocyclic cyclobutenes ring-opening reactions to build a systematic study to understand the nature of the chemical bond, electronic reorganization, and stereochemistry prediction in order to recognize the validity of the QTAIM and stress tensor scalar and vector measures.…”