Solid state structure of NH‐pyrazoles not easily amenable to crystal structure determinations: The case of 3(5)‐phenyl‐5(3)‐methylpyrazole and 3,5‐diphenyl‐4‐methylpyrazole

The structures of 3(5)‐methyl‐5(3)‐phenylpyrazole (polymorph B ) and 3,5‐diphenyl‐4‐methylpyrazole in the solid state cannot be determined by X‐ray crystallography due to the lack of suitable monocrystals. The combined use of CPMAS nmr, DSC and powder diffraction provides information about the behaviour of these pyrazoles in the solid state, particularly, about N‐H ⃛N intermolecular proton transfer. 3(5)‐Methyl‐5(3)‐phenylpyrazole is an example of the influence of polymorphism on the proton exchange since polymorph A (a tetramer formed by a mixture of both tautomers) presents the phenomenon but polymorph B (formed exclusively by 3‐phenyl‐5‐methyl tautomer) is devoid of it.