The non-additivity of the methyl groups in the single-electron lithium bond was investigated using ab initio calculations at the B3LYP/6-311＋＋G＊＊ and UMP2/6-311＋＋G＊＊ levels. The strength of the interaction in the H3C… LiH, H3CH2C… LiH, （H3C）2HC… LiH, and u v （H3C）3C… LiH complexes was analyzed in term of the geometries, energies, frequency shifts, stabilization energies, charges, and topological parameters. It is shown that （H3C）3C radical with LiH forms the strongest single-electron lithium bond, followed by （H3C）2HC radical, then H3CH2C radical, and H3C radical forms the weakest single-electron lithium bond. A positive non-additivity is present among methyl groups. Natural bond orbital and atoms in molecules analyses were used to estimate such conclusions. Furthermore, there are few linear/nonlinear relationships in the system and the interaction mode of single-electron Li- bond is different from the single-electron H-bond and single-electron halogen bond.
