An Analysis of the Isomerization Energies of 1,2-/1,3-Diazacyclobutadiene, Pyrazole/Imidazole, and Pyridazine/Pyrimidine with the Turn-Upside-Down Approach

Abstract

The isomerization energies of 1,2- and 1,3-diazacyclobutadiene, pyrazole and imidazole, and pyridazine and pyrimidine are 10.6, 9.4, and 20.9 kcal/mol, respectively, at the BP86/TZ2P level of theory. These energies are analyzed using a Morokuma-like energy decomposition analysis in conjunction with what we have called turn-upside-down approach. Our results indicate that, in the three cases, the higher stability of the 1,3-isomers is not due to lower Pauli repulsions but because of the more favorable σ-orbital interactions involved in the formation of two C-N bonds in comparison with the generation of C-C and N-N bonds in the 1,2-isomers.

Introduction and theoretical investigation of new azafullerene structures with nitrogen belts

“…Regardless of this, El-Hamdi et al [35], showed that the Pauli repulsions due to N-N lone-pair repulsion are not responsible for the lower stability of 1,2-diazabenzen, -cyclobutadiene and pyrazole compared to their 1,3-counterparts, because it is recompensed by the low Pauli repulsions of C-C bond. According to their results, the σ-skeleton of the molecule and different electrostatic and orbital interactions of C-N, C-C and N-N σ-bonds play very important roles in the isomer stabilization [35].…”

Planar vs. three-dimensional X62−, X2Y42−, and X3Y32− (X, Y = B, Al, Ga) metal clusters: an analysis of their relative energies through the turn-upside-down approach

“…A similar scheme based on the same EDA approach was used by Frenking and coworkers 54,55 and by some of us 36,37,56 to estimate the strength of p-cyclic conjugation in typical (anti)-aromatic organic compounds and in metallabenzenes and metallacyclopentadienes. Let us mention here that, as already mentioned in the introduction, some of the analysed metal clusters exist experimentally as lithium salts.…”

Aromaticity and Magnetic Properties of 1‐ and 2‐Indenones and Their Aza Derivatives

“…The relative stabilities discussed above can be further analyzed by means of an energy decomposition analysis (EDA) 57–62. Scheme shows that the 1‐oxo and the corresponding 2‐oxo isomers can be formed from the same two fragments by simply turning the fragment on the right upside‐down 4,63,64. Thus, each pair of isomers have been analyzed through the EDA analysis, with the corresponding values enclosed in Table 8.…”