The hydrogen bond stabilizing effect in enammonium salts of captodative aminoalkenes containing a carbonyl group

Enhanced stability of enammonium salts of captodative carbonyl-containing aminoalkenes as compared to the salts of simple enamines is discussed on the basis of 1H and 13C NMR, IR, UV spectroscopy and the results quantum chemical calculations. Stabilization of the Nprotonated form of captodative aminoalkenes is due to either intramolecular (NHþ· · ·OyC) or intermolecular (NHþ· · ·Solv or NHþ· · ·X2) hydrogen bonding, whereas the C-protonated form is destabilized due to umpolung of the carbon–carbon double bond. The formation of bifurcated (three-centered) hydrogen bond between the enammonium cation and the solvent is demonstrated. The three-centered solvate complex is characterized by nonclassical dependence of the chemical shift of the bridging hydrogen atom from the proton-acceptor power of the solvent. q 2003 Elsevier B.V. All rights reserved.