NATURE OF HYDROGEN-BONDS FORMED BY PHENOL DERIVATIVES AND N,N-DIMETHYLANILINE IN APROTIC-SOLVENTS - LOW-TEMPERATURE NMR-STUDIES

Phenols interact with NN-dimethylaniline to produce complexes with molecular (O-H...N) and ion-pair (O-... H-N-) hydrogen bonds. The degree of association and the character of the hydrogen bonds depends strongly on the solution temperature and DELTApK(a) [=pK(a) (protonated base) - pK(a) (phenol)] in water. The tautomeric equilibrium, O-H...N reversible O-...H-N+, which is slow on the NMR timescale, has been recorded in the 0.4 to -0.5 DELTApK(a) range below 140 K. Thermodynamic and kinetic quantities of the equilibrium were calculated from H-1 NMR spectra of the 2,3,5,6-tetrachlorophenol complex. The thermodynamic quantities for the 2,6-dichloro-4-nitrophenol complex were obtained from C-13 NMR results.