I have just noticed unexpected links between two old posts, one about benzene, one about diphenyl magnesium and a link to August Kekulé. ^† Click for 3D The post about benzene dealt with the apparently simple issue of why all the C-C bonds are of equal length. The answer, in brief is purely because of the σ-electrons. If the π-electrons had their way, benzene would have three short and three long C-C bonds.