Rank the following compounds in order of decreasing reactivity to aromatic electrophilic bromination.
I. benzene
II. toluene
III. benzoic acid
IV. phenol
The groups on the benzene could be either activating (make the benzene ring more reactive) or deactivating (make the benzene ring less reactive). To do this problem, all we have to do is find these groups in the chart below that identifies the groups as activators and deactivators and breaks them into: strong, moderate, weak. Toluene has a CH3 group on the benzene which is R (any alkyl group) on the chart and a weak activator. Benzoic acid has a COOH group which is a moderate deactivator. Phenol has an OH group which is a strong activator. Therefore, the rank should be phenol as the most reactive, followed by toluene then benzene and finally benzoic acid.
