For example, the reaction of benzoic acid leads to 2,5-cyclohexadienecarboxylic acid, which can be rationalized on the basis of the carboxylic acid stabilizing an adjacent anion: Alkene double bonds are only reduced if they are conjugated with the arene, and occasionally isolated terminal alkenes will be reduced. The effect of electron-withdrawing substituents on the Birch Reduction varies. In contrast to the examples with electron donating substituents, the case with withdrawing groups is more readily obvious. Thus, as depicted below, the structure of the penultimate dianion D is characterized by its being subject to trapping by alkyl halides.