Proton transfer and secondary deuterium isotope effect in the 13C NMR spectra of ortho-aminomethyl phenols

The temperature dependence of the deuterium isotope effect on the 13C NMR signals for various positions in the phenyl ring of 2-(N,N-diethylaminomethyl) tetrachlorophenol was studied in the moderately polar solvent CH2Cl2. The critical temperature, Tc = 245 K, corresponds to the compensation of opposite effects for non-proton-transfer and proton-transfer (PT) forms existing in equilibrium. The UV spectra show that the contribution of the PT form at 245 K amounts to 20 ± 5%. Semi-empirical calculations taking into account the Onsager reaction field allowed us to discuss the role of permittivity and dimerization of polar PT forms in the charge separation.