1H and 13C NMR and FT-IR studies of the interaction between 1,8-bis(dimethylamino)naphthalene and 3,5-dichlorophenol

Abstract

The ¹H and ¹³C NMR spectra of the complex between 1,8-bis(dimethylamino)naphthalene and 3,5-dichlorophenol have been studied at temperatures between 30 °C and –70 °C in CD₂Cl₂ and at different acid to base concentration ratios. At a temperature of –60 °C a splitting of the ¹H and ¹³C signals of DMAN and DMANH⁺ is observed. The protonation degree deduced from the NMR data and the intensity of the Bohlmann bands are in very good agreement. At a temperature below 8 °C, a splitting (2.6 Hz) of the methyl protons caused by spin–spin coupling with the (NHN)⁺ bridge protons is observed. Comparison with literature data and with the coupling constant determined in this work for protonated N,N-dimethylaniline suggest that the potential surface of the NHN⁺ cation includes two symmetrically situated wells between which fast proton migration takes place.