Association and relative acidities of 2-substituted 5-trifluoroacetylpyrroles
The acidities of 2-substituted 5-trifluoroacetylpyrroles were studied by IR spectroscopy from the shift of the frequency of the NH stretching vibration (ΔνNH) in the presence of dimethylformamide (DMF) relative to the band of vibrations of free NH. The existence of a correlation relationship between ΔνNH and ∑σI constitutes evidence that the acidities of pyrroles are determined primarily by the inductive effect of the substituents in the 2 and 5 positions of the pyrrole ring. The low probability of the formation of an intramolecular NH... O=C hydrogen bond in the investigated molecules was demonstrated.