1H and 13C NMR studies of proton transfer in intramolecular hydrogen bonds in substituted 2‐diethylaminomethylphenol N‐oxides

Eleven substituted 2‐diethylaminomethylphenol N‐oxides were studied in CDCl3 solutions by 1H and 13C NMR spectroscopy. The 1H chemical shifts of the intramolecular hydrogen‐bonded proton and the Δ14 values obtained from the 13C signals were considered as a function of the pKa values of the parent phenols. The 1H chemical shift of the hydrogen‐bonded proton shows a maximum at pKa ≈ 7. This result agrees well with the turning point of the curve if Δ14 is plotted as a function of the pKa of the parent phenols. All these results agree well with recently obtained Fourier transform IR results. With the system with the strongest hydrogen bond (pKa ≈ 7) a broad, flat, single‐minimum proton potential or a double‐minimum proton potential with a small barrier is present. With this system the deshielding of the proton in the intramolecular hydrogen bond is strongest.