On the Protonation and Deuteration of Simple Phenols**

Abstract In analogy with the reaction of phenols with very strong super acids, these compounds can be protonated by the weaker super acid trifluoroacetic acid (TFA) and trifluoromethanesulphonic acid (TFS) also giving rise to the formation of OH and/or ring protonated products, which can be identified unambiguously by means of 1 HNMR spectroscopy. The same reactions are possible with the deuterated acids TFA‐d and TFS‐d. However, from these reactions, additional information on the proton and deuterium attack at different positions in the phenolic compounds is possible not detectable by the hitherto used non‐deuterated acids. Moreover, the reaction of phenols with these deuterated acids allows the preparation of partially or fully deuterated phenols that are also important as markers in biological application and material chemistry.