The H-1, C-13 and 15N NMR spectra of 4-bromo-6-diethylaminomethyl-2-R-iminomethyl-phenol have been recorded in CDCl3, in temperatures of 230-300 K. The presence of equilibrium between the two competitive OH . . . NCH2 and OH . . .N=C intramolecular hydrogen bonds has been found. The rotation of the OH group slows down at 230 K (in the NMR-time scale). Compound 1 (R=NC2H5) exists mainly with the OH group engaged in the intramolecular hydrogen bond to the imine-N atom (85%). The weakening the hydrogen bond by substitution of the N-alkyl by the N-aniline group (compound 2) increases the population of the Mannich type form (to 40%). (C) 2001 Elsevier Science B.V. All rights reserved.