Evidence for a Low-Lying Second Potential Minimum in Hydrogen-Bonded Systems

Abstract

The spectra of phenol-d and p-nitrophenol-d associated with amines in chloroform show, in the region of the stretching fundamental, a band splitting that can be interpreted in terms of a double minimum potential for the proton. For p-nitrophenol and a base as strong as triethylamine, both the infrared and visible spectra show that the associated complex consists of a tautomeric equilibrium between proton transferred and nonproton transferred species. For these systems also, the potential experienced by the proton shows a double minimum. It appears, therefore, that for hydrogen-bonded systems of the type dealt with here in nondissociating solvents the hydrogen-bonding proton will experience a double minimum potential for all strengths of association.