Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

¹³C and ¹⁵N NMR spectra have been measured of eleven 3-methyl-1-phenylpyrazole-4,5-dione 4-(4'-substituted phenyl)hydrazones (I). The ¹³C chemical shifts of the non-substituted compound I have been assigned with the use of the ¹J(¹³C, ¹³C) coupling constants obtained from the 1D-INADEQUATE spectrum. The greatest changes in chemical shifts of the compounds I connected with the substituent at 4'-position have been observed for the nitrogen atoms N_α, N_β, N₂ and carbon C(4). These substitution chemical shifts have been correlated with the substituent constants by means of the equations SCS = ρ₁σ₁ + ρ_Rσ_R + const., where σ_R means one of the values σ_R⁰, σ_R^BA, σ_R^-, or σ_R⁺. The best correlations have been obtained for the combinations N_α - σ_R^BA, N_β - σ_R^-, N₂ - σ_R⁰, and C(4) - σ_R⁰. The ¹⁵N substituent chemical shifts of the nitrogen atoms N_α and N_β of compounds I have been compared with the analogous values of 4-substituted trans-azobenzenes.