The potential energy shape for the proton motion in protonated naphthalene proton sponges (DMAN-s) and its manifestations

Abstract

The problem of the low-barrier hydrogen bond in protonated naphthalene proton sponges is reviewed. Experimental data related to the infra-red and NMR spectra are presented, and the isotope effects are discussed. An unusual potential for the proton motion that leads to a reverse anharmonicity was shown: The potential energy curve becomes much steeper than in the case of the harmonic potential. The isotopic ratio, i.e., νH/νD (ν-stretching vibration frequency), reaches values above 2. The MP2 calculations reproduce the potential energy curve and the vibrational H/D levels quite well. A critical review of contemporary theoretical approaches to the barrier height for the proton transfer in the simplest homoconjugated ions is also presented. © 2010 Springer Science+Business Media B.V.