Synthesis, spectroscopic characterisation and X-ray analysis of regioisomeric 1,3,5-trisubstituted pyrazoles

A new series of regioisomeric 1,3,5-trisubstituted pyrazoles 7-9(a,b) have been synthesized by the reaction of β-diketones (4-6) with methyl hydrazine in ethanol. All the compounds are characterised by the FT-IR, ¹H, ¹³C NMR and mass spectrometry. The crystal structure of compounds 7a, 7b and minor isomer 8b have been determined by X-ray single crystal analysis which showed either of the substituted groups attached to pyrazole ring are essentially non-planar to the central pyrazole ring. Addition of trace amounts of acetic acid during the synthesis of compound 8 resulted in an unexpected compound 10 which is characterised by the X-ray single crystal analysis and is essentially planar. However, crystal structure of 10 is already reported. All structures are further stabilized by the classic and non-classic inter- and intramolecular hydrogen bonding.