Abstract Nucleophilic aromatic substitution by [18 F] fluoride ion has been demonstrated on rings containing electron donating groups in addition to the necessary electron withdrawing and leaving groups. The reaction of 18 F− with a series of aromatic nitro aldehydes having protected hydroxyl substituents on the ring was studied. The reactivity of the aromatic ring towards nucleophilic substitution to give 18 F-labeled aromatic fluoroaldehyde derivatives ...