Nuclear Magnetic Resonance Studies of Hydrogen-Bonded Complexes of Tri-N-Octylamine Hydrochloride with Chloroform

Abstract

In this study nuclear magnetic resonance spectroscopic techniques were employed to investigate the hydrogen­bonded complex of tri-n-octylamine hydrochloride with chloroform. Concentration studies of tri-n-octylamine hydrochloride in 1,2 dichloroethane, carbon tetrachloride, and cyclohexane with a constant chloroform concentration of 0.09 molar showed a weak but measurable interaction between the chloroform and the anion of the amine salt. The concentration dependence of the chloroform proton shielding was analyzed to reveal shieldings in the complex, and equilibrium constants. The concentration dependence of the chloroform proton shielding was also studied at various temperatures to obtain enthalpy and entropy data for the formation of the hydrogen-bonded complex. The concentration dependence of the N-H proton shielding showed that in the concentration region studied, 0.1-0.5 molar, the anion-cation hydrogen-bond of the tri-n-octylamine hydrochloride is strong and does not dissociate. Also, examination of the N-H proton chemical shifts revealed qualitatively that the tri-n-octylamine hydrochloride in 1,2 dichloroethane exists primarily as a monomer, and in carbon tetrachloride as a trimer, and in cyclohexane probably as some higher n-mer. Analysis of the N-H proton chemical shifts in carbon tetrachloride gave an equilibrium constant for the trimeric self-association of tri-n-octylamine hydrochloride of the order of approximately 25 liter/mole.