Structure investigation of intramolecular hydrogen bond in some substituted salicylaldehydes and 4-aminoantipyrine derivatives in solution and in the solid state

Seven imine derivatives obtained by condensation of appropriate aldehydes and salicylaldehydes with 4-aminoantipyrine were investigated in terms of intramolecular hydrogen bond structure. On the base of 1H, 13C and 15N NMR measurements in solution and in the solid state we found out that all compounds which can form such structure exist as OH forms with strong H-bonds to nitrogen atom. The structure conclusions taken from NMR study were confirmed by pKa measurements. Surpassingly, the positions of protons in H-bridges only very slightly depend on the substituents in aldehyde used for condensation and on the phase (solution vs. solid state). The influence of antipyrine moiety seems to be the major factor defining H-bond structure.

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► We synthesized seven o-hydroxy Schiff bases from 4-aminoantipyrine.
► We performed combined solution 1H, 13C and 15N and solid state 13C and 15N NMR spectra.
► The positions of tautomeric equilibria of Schiff bases were defined.
► The pKa measurements were done to compare with NMR data.