35Cl nuclear quadrupole resonance studies of pentachlorophenol–amine hydrogen-bonded complexes

Abstract

A series of hydrogen bonded complexes of pentachlorophenol with various N bases, covering a wide range of ΔpK_a values, was investigated using ³⁵Cl n.q.r. The average frequencies of ³⁵Cl n.q.r. of these complexes were compared with those of pentachlorophenol, tetrabutylammonium pentachlorophenolate and tetrabutylammonium bis-pentachlorophenolate. The changes of average frequencies as a function of ΔpK_a are very similar to the dipole moment changes with hydrogen bond formation as a function of ΔpK_a, but in solids the range of inversion is shifted to lower ΔpK_a values. The region in which the dielectric and spectroscopic anomalies are observed may be formally attributed to the existence of the proton transfer equilibrium.