Molecular structure and tautomerism of 3,5-bis(4-methylpyrazol-1-yl)-4-methylpyrazole

Abstract

The title compound C12N6H14, 1, crystallizes in the space group P21/n (a = 8.222(2) Å, b = 27.336(8) Å, c = 5.574(2) Å, α = 90.00°, β = 100.97(4)°, γ = 90.00°), Z = 4, d = 1.308 g cm−3. The conformation about the N—C bonds linking the pyrazole rings can be defined as EZ, with "pyridine-like" nitrogen atoms in an anti disposition [Formula: see text] and "pyridine-like" and "pyrrole-like" nitrogen atoms in a syn disposition [Formula: see text] with regard to the central pyrazole. Intermolecular hydrogen bonds between the central and the terminal pyrazole ring of configuration Z form centrosymmetric dimers. They pack in sheets nearly parallel to the (−2 3 1) plane. Its tautomerization barrier has been determined in methanol-d4; the value, 11.9 kcal mol−1, is similar to those of 3,5-dimethyl-4-chloropyrazole (12.8 kcal mol−1) and 3,5-dimethyl-4-nitropyrazole (12.1 kcalmol−1). These values together with the shape of the conformational potential surface (calculated using the AM1 Hamiltonian) suggest that, in compound 1, prototropy and rotation about the N—C bonds linking the three pyrazole rings take place simultaneously.