Ab initio calculations with STO-3G method were carried out on isomers of isobutylene dianion and dilithioisobutylene, and geometry, energy and Mulliken population were discussed. Energy of reaction, ${Delta}$E, for isodesmic processes involving these species and relative heats of formation, ${Delta}H_f$, estimated with ${Delta}$E have shown that the contribution of "Y-aromaticity" to the structural stabilization of Y-type dianion is a tenuous one but the alkylation appears to proceed via the Y-type dilithio compound