A stepwise mechanism for this reaction has been proposed where a pair of electron additions occur, each addition followed by abstraction of a proton from solution, proceeding through a radical anion intermediate before reaching the neutral final product.  Substituents on the target compound can control the regioselectivity of the reaction; electron-donating groups favor pr
A stepwise mechanism for this reaction has been proposed where a pair of electron additions occur, each addition followed by abstraction of a proton from solution, proceeding through a radical anion intermediate before reaching the neutral final product.  Substituents on the target compound can control the regioselectivity of the reaction; electron-donating groups favor protonation at an unoccupied site meta to the substituents, while electron-attracting substituents favor para protonation. Reaction conditions typically feature an alkali metal dissolved in liquid ammonia, which provide the electrons and protons, respectively. FTP, what is this reaction that reduces a benzene ring to 1,4-cyclohexadiene?
A stepwise mechanism for this reaction has been proposed where a pair of electron additions occur, each addition followed by abstraction of a proton from solution, proceeding through a radical anion intermediate before reaching the neutral final product.  
the Birch reduction