Solvatochromism of heteroaromatic compounds: III. 3(5)-nitropyrazole

Solvatochromism of, 3(5)-nitropyrazole and its anion was studied in inert, protophilic, and protophobic media. The position of the long-wave absorptio n band was described in terms of the general and group Kamlet-Taft paramete rs. Differences were revealed in specific solvation through formation of li near and cyclic H-complexes, as well as in the effect of nonspecific solvat ion on the spectra of the neutral molecule, its anion, and H-complexes. Acc ording to nonempirical calculations with the 6-31G* basis set, the cyclic H -complex formed by 3-nitropyrazole with one water molecule is 1.0 kcal/mol more thermodynamically favorable than the H-complex of the same composition .