Far-IR study of the hydrogen-bond vibration of intramolecular bonds in substituted 2-diethylaminomethylphenol N-oxides, as a function of the pKa of the phenolic group

Abstract

The intramolecular hydrogen-bond vibration in R-substituted 2-diethylaminomethylphenol N-oxides in the farinfrared region has been studied. With decreasing pK_a value of the phenolic group this vibration shifts first towards higher and then towards lower wavenumbers. The proton is transferred within the OH⋯ON⇌O^–⋯H⁺ON hydrogen bond with increasing acidity of the phenolic group. This bond is strongest for R = 4 -NO₂, and the hydrogen bond vibration is very broad in this system. It has been found that the change of the position of the hydrogen bond vibration is independent of the mass of the substituents. All results in this work agree very well with results obtained for corresponding intermolecular hydrogen bonds.