The structure and dynamic properties of 1H-pyrazole-4-carboxylic acids in the solid state

The structure of three simple pyrazole-4-carboxylic acids unsubstituted in position 1 (NH derivatives) 1H-pyrazole-4-carboxylic acid (1), 3(5)-methyl-1H-pyrazole-4-carboxylic acid (2) and 3,5-dimethyl-1H-pyrazole-4- carboxylic acid (3) are discussed based on crystallographic results (two new structures) and solid-state NMR (CPMAS). Compounds 1 and 3 present polymorphism and one of the polymorphs of each compound shows solid-state proton transfer (SSPT). Compound 2 presents tautomerism that has been studied by NMR, both in the solid-state and in solution at low temperature. © by Oldenbourg Wissenschaftsverlag, München.Peer Reviewe