(1)H-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 (1)H-MAS-NMR Spectra

Chemical shifts (CS) of the (1)H nucleus in N···H···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 (1)H-NMR with the magic-angle-spinning (MAS) method. Employing N-Bases with a wide range of pK(a) values (0.65–10.75), (1)H-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 pK(a) values in a range of ΔpK(a) < 0 [ΔpK(a) = pK(a)(N-Base) - pK(a)(chlorophenols)] and decreased when ΔpK(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 (1)H-MAS-NMR spectra were observed in PCP–2-amino-3-methylpyridine. 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 (1)H-MAS-NMR peaks.