During
recent years our research group has studied the nature of chemical bonds
using the background studied by Silvi and collaborators using the bond
progression theory as an extension of Bader´s work and the scalar field
related to the electron localization function (ELF)17–23. These studies have proposed the electronic
reorganization as a pseudo radical process instead pericyclic process
suggested by Woodward-Hoffmann rules 24–26.
Additionally, we use the analysis of natural bond orbitals (NBO), the
quantum theory of atoms in molecules (QTAM), and the electronic
structure principles such as minimum polarizability, minimum
electrophilicity and, maximum hardness presenting new insights into the
process of electronic reorganization agree with experimental data27–30.
Scheme 1. Ring-opening reaction of Cyclobutenes studied
Table 1. Thermal ring-opening reaction of cyclobutenes, the
reaction set analyzed in this study.
Relative Energy (Kcal/mol) △TS
Reaction Reactant (substituents) TSIC TSOC (TSIC-TSOC)
Stereochemistry Ref.of Product
R1 1-chlorocyclobut-1-ene 41.425 41.425 0.000 —31
R2 3-chloro-4-methylcyclobut-1-ene 49.411 42.642 +6.769E,Z 32
R3 3-chloro-4-methoxycyclobut-1-ene 53.973 42.763 11.210E,Z 32
R4 3-methoxy-4-methylcyclobut-1-ene 44.794 51.323 -6.529E,E 32
Table 1 shows the reaction set analyzed in this study (seeFigure 1 ). There is molecular variety in the reaction set
analyzed from reactions without stereochemistry and competitive
reactions with E, Z stereochemistry. The main aim is to build a
systematic study to understand the nature of the chemical bond,
electronic reorganization, and stereochemistry prediction according to
the experimental data.