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 data^27–30.

Scheme 1. Ring-opening reaction of Cyclobutenes studied

Table 1. Thermal ring-opening reaction of cyclobutenes, the reaction set analyzed in this study.

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.