AbstractHigh yield single step preparation of 4′‐18F‐spiperone by18F‐ for NO2exchange in highly basic conditions fails when using 4′‐NO2‐spiperone as a precursor. This compound moreover inhibits radiofluorination of highly activated molecules in mentioned conditions. Inhibition is not provoced by ketalised analogues of the butyrophenone. This led to assume that enolisation of the butyrophenone was responsible for those phenomena. The assumption is supported by the fact that the results of inhibition experiments fit to a theo