FT-IR and NMR stedies of proton sponge character of Cis-1,2-bis(diethylaminomethyl)cyclohexane

Cis-1,2-bis(diethylaminomethyl)cyclohexane (DEAMCH) was synthesized and its pK-a values in acetonitrile were measured. Dual behevioral of DEAMCH was observed in the reaction with various acids: HClO4, 4-tert-butylphenol, 4-cyanophenol and pentachlorophenol (PCP) in acetonitrile and acetone-d-6 solutions, respectively, when studied by FT-IR as well as (1)H, (13)C and (15)N NMR spectroscopy. An intramolecular NHN(+) hydrogen bond was found in 1:1 complex of DEAMCH with HClO4 in solution. This hydrogen bond was, however, weaker than those previously observed in other protonated proton sponges. In complexes of DEAMCH with 4-cyanophenol both NHN(+) intramolecular hydrogen bond and structurally symmetrical intermolecular homoconjugated (OHO)(-) hydrogen bonds were formed. These properties of DEAMCH demonstrate its proton sponge like character. On the other hand, in complexes of DEAMCH with more acidic phenol such as PCP intermolecular hydrogen-bonded complexes are formed, in which the OH protons are localized at the amino groups. For these O(-)...HN(+) hydrogen bonds a strongly asymmetrical double minimum proton potential with the well at the N atom is present, characteristic of complexes having no proton sponge like character.