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Note | Regular issue | Vol 65, No. 11, 2005, pp.2753-2761
Published online, 16th September, 2005
DOI: 10.3987/COM-05-10499
Comparative Structural Studies of 4-Diazopyrazole Derivatives by X-Ray Diffraction and Theoretical Investigation

Giuseppe Daidone,* Benedetta Maggio, Maria Valeria Raimondi, Gabriella Bombieri, Nicoletta Marchini, and Roberto Artali

*Department of Pharmaceutical Chemistry and Technology, University of Palermo, Via Archirafi 32, 90123 Palermo,

Abstract

The X-Ray crystal and molecular structures of the 4-pyrazol derivatives 3-methyl-4-diazo-5-benzamido-1H-pyrazole (4) and 3-benzamido-5-methyl-1H-pyrazole (3) have been determined. A dimeric structure has been found for the first and polymeric for the second. A comparison of 4 with 1,3-dimethyl-4-diazo-5-benzamido-1H-pyrazole (2) shows differences in the geometrical parameters of the pyrazole ring due to electron delocalization in 2 consequent to the nitrogen negative charge in the latter. Theoretical investigation at the density functional theory (DFT) level shows difference in the molecular electronic distribution of 2 and 4, in agreement with the structural parameters and the IR stretching frequencies of the respective carbonyl moieties.