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Analysis of the Effects of N-Substituents on Some Aspects of the Aromaticity of Imidazoles and Pyrazoles

Posted September 5th, 2013 by ccurutchet
TitleAnalysis of the Effects of N-Substituents on Some Aspects of the Aromaticity of Imidazoles and Pyrazoles
Publication TypeJournal Article
Year of Publication2011
AuthorsCurutchet, C, Poater J, Sola M, Elguero J
JournalJournal of Physical Chemistry A
Volume115
Issue30
Pagination8571 - 8577
Date Published2011
ISBN Number1089-5639
Keywordsab-initio, atoms, benzene rings, density, electron delocalization, heterocycles, independent chemical-shifts, molecular-orbital methods, multicenter bond indexes, nics
AbstractThe influence of the N-substituent on the aromaticity of azoles is a subject that has not yet been addressed in detail, in contrast to the good understanding of the corresponding C-substitution. In the present work, we analyze the aromaticities of a series of 1,2- and 1,3-azoles (pyrazoles and imidazoles, respectively) with the N-substituents NH(2), OH, Cl, SH, H, NO(2), CN, SO(2)F, SO(2)CF(3), and N(SO(2)CF(3))(2), which are also compared with the aromaticities of the corresponding substituted benzene series. The larger stability of the imidazole ring is due not to a higher aromaticity, but rather to the weakness of the N N bond in the pyrazole series. The aromaticity of azoles was found to be significantly less robust to N-substitutions than that of their C-substituted benzene counterparts.