The Unusual Properties of 5‐Methyl‐4,5,6,7‐Tetrahydro‐1H‐Indazole in the Solid State

The crystal structure of the title compound was determined by X‐ray analysis at 200 K. Three independent molecules form a trimer joined by strong and linear N‐H … N hydrogen bonds. There is another centrosymmetrically related trimer in the unit cell. Both tautomers (1 H and 2 H ) are present in each trimer. Disorder of the N H protons involved in the N‐H … N hydrogen bonds has been observed. Solid‐state 13 C CPMAS NMR was used to establish the dynamic nature of the N H ‐proton disorder, the title compound being the first example of proton transfer in a tautomeric mixture of pyrazoles with an equilibrium constant other than 1.