Deuterium isotope effects on 15N chemical shifts of double Schiff bases in the solid state and solution

The proton transfer equilibrium in a series of double Schiff base derivatives of trans‐1,2‐diaminocyclohexane in solution and the solid state was studied by means of 15N NMR spectroscopy and analysis of the deuterium isotope effect on the chemical shifts Δ15N(D). The presence of a proton transfer equilibrium in the N‐2‐hydroxynaphthylidene moieties of the Schiff bases studied in the solid state at room temperature was evidenced. The results confirmed the interrelation of the two hydrogen bonds in double Schiff base derivatives of trans‐1,2‐diaminocyclohexane.