cis-3,4-di-Cl (TSOC). Mechanism of Electrocyclic Reactions, Stereoselectivity in Cyclobutenes.
Intrinsic Reaction Coordinate calculated by means the
software Gaussian 16, the B3LYP/6-311G(d,p)
method/basis-set have been used for the calculation.
R E F E R E N C E:
Title: New insights about electronic mechanism of electrocyclic
reactions: theoretical study about stereoselectivity in
cyclobutenes.
Alejandro Morales-Bayuelo, Jesús Sánchez-Márquez.
Heliyon 7 (2021) e06675
https://doi.org/10.1016/j.heliyon.202...
Published by Elsevier Ltd.
Open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/b....
A B S T R A C T:
This work presents the study of a series of electrocyclic
reactions with the main aim of obtaining new insights into
the reaction process along IRCs. The energy variation of
the different reaction paths as well as the different
transition states have been calculated. These trends are
according to the experimental data. The natural bond
orbitals have been obtained and the second order
perturbational theory analysis has been carried out to
determinethe main charge transfers due to delocalization.
Bond reactivity indexes have been used to describe the
reactivity mechanism in a local way. These reactivity
indexes are also based on NBOs and this has made it possible
to connect the results of the indexes with the previous
analysis. To determine quantitatively the bond structure,
we used the quantum theory of atoms in molecules and we
have hereby completed the information obtained from the
NBO analysis. Finally, we used the Hirshfeld population
analysis as an approximation to understand how the load
density changes in the different reaction pathways, and
we have connected these variations with the information
obtained from the bond structure.
The results has found that the reaction path with the
lowest energy barrier Transition State Inward Conrotatory
(TSIC) or Transition State Outward Conrotatory (TSOC) is
determined by two magnitudes: the charge donations
by delocalisation of the substituents (which we obtained
from the Second Order Perturbational Theory Analysis of
the NBOs) and in the case that these donations were very
similar, the non-covalent interactions dominated (which
we studied by means of the interaction energies of the
Hirshfeld charges). Additionality, the most important
factor influencing the lower energy reaction path was
the interaction of lone pairs of the substituents with
the σ*(C–C) bond that is broken at the opening of the cycle.
The alignment of these lone pairs with the C–C bond favours
charge donation between them and, as can be seen in the
discussion, this alignment varies depending on whether
the structure is TSIC and TSOC.