SOLVATION OF 4-NITROPYRAZOLES ACCORDING TO UV SPECTROSCOPY DATA

The dependence of the energies of intramolecular charge-transfer elect ron transitions in 1,3,5-trimethyl-4-nitropyrazole, 4-nitropyrazole, a nd its anion on the dielectric and acid-base properties of solvents wa s analyzed. The dipole moments of these species in the excited state a re larger than those in the ground state. The nonspecific solvation is accomplished through dipole-dipole interactions. 4-Nitropyrazole, whi ch possesses acidic properties, is also solvated by the mechanism of h ydrogen bonding with the solvent, which acts as a base. The strength o f the hydrogen bond increases on going from the ground to the electron -excited state. The 4-nitropyrazole anion is a base, and its hydrogen bonds with the solvent are stronger in the ground state. The mechanism of specific solvation of the molecule and the anion of 4-nitropyrazol e during electronic excitation is discussed.