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

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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.