Birch Reduction of Benzene
According to the article on Birch Reduction on the Organic Chemistry portal: 

The question of why the 1,3-diene is not formed, even though it would be more stable through conjugation, can be rationalized with a simple mnemonic. When viewed in valence bond terms, electron-electron repulsions in the radical anion will preferentially have the nonbonding electrons separated as much as possible, in a 1,4-relationship.

http://www.organic-chemistry.org/namedreactions/birch-reduction.shtm