1H-MAS-NMR Chemical Shifts in Hydrogen-Bonded Complexes of Chlorophenols (Pentachlorophenol, 2,4,6-Trichlorophenol, 2,6-Dichlorophenol, 3,5-Dichlorophenol, and p-Chlorophenol) and Amine, and H/D Isotope Effects on 1H-MAS-NMR Spectra

Chemical shifts (CS) of the H-1 nucleus in N center dot center dot center dot H center dot center dot center dot O type hydrogen bonds (H- bond) were observed in some complexes between chlorophenols [ pentachlorophenol (PCP), 2,4,6- tricholorophenol (TCP), 2,6- dichlorophenol (26DCP), 3,5- dichlorophenol (35DCP), and p- chlorophenol (pCP)] and nitrogen- base (N- Base) by solid- state high- resolution H-1- NMR with the magic- angle- spinning (MAS) method. Employing N- Bases with a wide range of pK(a) values (0.65- 10.75), H-1- MAS- NMR CS values of bridging H atoms in H- bonds were obtained as a function of the N- Base's pK(a). The result showed that the CS values were increased with increasing pKa values in a range of Delta pKa < 0 [Delta pK(a) = pK(a)(N- Base) - pK(a)(chlorophenols)] and decreased when Delta pK(a) > 2: The maximum CS values was recorded in the PCP (pK(a) = 5.26)- 4- methylpyridine (6.03), TCP (6.59)- imidazole (6.99), 26DCP (7.02)- 2- amino- 4- methylpyridine (7.38), 35DCP (8.04)- 4- dimethylaminopyridine (9.61), and pCP (9.47)- 4- dimethylaminopyridine (9.61) complexes. The largest CS value of 18.6 ppm was recorded in TCP- imidazole crystals. In addition, H/D isotope effects on H-1- MAS- NMR spectra were observed in PCP- 2- amino- 3methylpyridine. Based on the results of CS simulation using a B3LYP/6- 311+ G** function, it can be explained that a little changes of the N- H length in H- bond contribute to the H/D isotope shift of the H-1- MAS- NMR peaks.