35Cl nuclear quadrupole resonance and infrared spectroscopic studies of 2,6-dichloro-4-nitrophenol–amine hydrogen-bonded adducts

Abstract

The charge distribution in hydrogen bridges of varying strengths in solid 2,6-dichloro-4-nitrophenol complexes has been studied using the n.q.r. technique. The dependence of the average ³⁵Cl n.q.r. frequencies, v_n.q.r., on the pK_a can be analysed in terms of the proton-transfer equilibrium. v_n.q.r. provides evidence for the existence of either a double-minimum potential function or one broad minimum. Infrared spectra of such complexes show very broad absorptions extending to the far-infrared, with numerous so-called ‘Evans holes’ and a weakening or complete disappearance of the protonic stretching vibration band in the usual range above 1800 cm^–1.