PYRAMIDAL NITROGEN INVERSION HINDERED BY A STRONG INTRAMOLECULAR HYDROGEN-BOND IN 2-DIETHYLAMINOMETHYLPHENOLS

In the H-1 NMR spectra of 2-diethylaminomethyl-3,4,6-trichlorophenol (1) below 260 K, an additional splitting of the CH2 signal was found, which can be ascribed to the hindered nitrogen inversion. In the molecule of the O-methylated derivative (2) this process is fast (on the NMR time-scale) down to 150 K. The frequencies and the activation parameters of the nitrogen inversion in (1) were measured by DNMR, which indicated that the inversion requires a preliminary stage of breaking an intramolecular hydrogen bond. The activation enthalpy, Delta H-inv(double dagger) of the inversion stage was evaluated as 28.5+/-6.7 kJ mol(-1).