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 an alysis at 200 K. Three independent molecules form a trimer joined by s trong and linear N-H ... N hydrogen bonds. There is another centrosymm etrically related trimer in the unit cell. Both tautomers (1H and 2H) are present in each trimer. Disorder of the NH protons involved in the NH ... N hydrogen bonds has been observed. Solid-state C-13 CPMAS NMR was used to establish the dynamic nature of the NH-proton disorder, t he title compound being the first example of proton transfer in a taut omeric mixture of pyrazoles with an equilibrium constant other than 1.