Skeletal formula of monomeric sec-Butyllithium. s-BuLi normally adopts a tetrameric structure as a solid, in solution, and in the gas phase, as shown in File:Sec-butyllithium-2D-skeletal.png. This monomeric depiction is not representative of the usual state of aggregation of s-BuLi, but is helpful in illustrating the difference between monomeric and oligomeric organolithium structures, and is often used to represent s-BuLi when drawing reaction mechanisms.