The gas-phase reactions of phenyl halides C6H5X (X = F-I) With FeO+ are examined using tandem mass spectrometry. The predominant dissociations involve losses of CO (X = F-I), HX (X = F, Cl), and X (X = I). For chlorobenzene 1, mechanistic insight is obtained from detailed labeling experiments, MS/MS studies, and comparison with structural isomers generated via independent routes. The experiments demonstrate that ring hydroxylation to a phenol, a reaction typical for FeO+ and unsubstituted benzene, does not occur for YFeO+. Instead, initial coordination of FeO+ at the functional group ("docking") predominates, thereby enforcing activation of the adjacent ipso and ortho positions, while meta and para positions do not participate.