DUGi

An analysis of the isomerization energies of 1,2-/1,3-diazacyclobutadiene, pyrazole/imidazole, and pyridazine/pyrimidine with the turn-upside-down approach

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@10256@@11390

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

We thank the following organizations for financial support: the Ministerio de Ciencia e Innovacion (MICINN, Project Nos. CTQ2008-03077/BQU, CTQ2008-06532/BQU, and CTQ2011-23156/BQU, Ramon y Cajal contract to J.P., and FPI fellowship to M.E.H.) and the DIUE of the Generalitat de Catalunya (project no. 2009SGR637). W.T. thanks FONDECYT (Grant No. 1109043). We acknowledge helpful comments from Prof. Dr. F. Matthias Bickelhaupt. Excellent service by the Centre de Supercomputacio de Catalunya (CESCA) is gratefully acknowledged

American Chemical Society (ACS)