The characteristics and structures of single-electron halogen bond complexes H3C…Br-Y(Y = H,CCH,CN,NC,C2H3) have been investigated by theoretical calculation methods.The geometries were optimized and frequencies calculated at the B3LYP/6-311++G level.The interaction energies were corrected for basis set superposition error(BSSE) and the wavefunctions obtained by the natural bond orbital(NBO) and atom in molecule(AIM) analyses at the MP2/6-311++G level.For each H3C…Br-Y complex,a single-electron Br bond is formed between the unpaired electron of the CH3(electron donor) radical and the Br atom of Br-Y(electron acceptor);this kind of single-electron bromine bond also possesses the character of a“three-electron bond”.Due to the formation of the single-electron Br bond,the C-H bonds of the CH3 radical bend away from the Br-Y moiety and the Br-Y bond elongates,giving red-shifted single-electron Br bond complexes.The effects of substituents,hybridization of the carbon atom,and solvent on the properties of the complexes have been investigated.The strengths of single-electron hydrogen bonds,single-electron halogen bonds and single-electron lithium bonds have been compared.In addition,the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier. The characteristics and structures of single-electron halogen bond complexes H3C ... Br-Y (Y = H, CCH, CN, NC, C2H3) have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP / 6- 311 ++ G level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyzes at the MP2 / 6-311 ++ G level .For each H3C ... Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH3 (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond to possesses the character of a “three-electron bond”. Due to the formation of the single-electron Br bond, the CH bonds of the CH3 radical bend away from the Br-Y moiety and the Br-Y bond elongates , giving red-shifted single-electron Br bond complexes. These effects of substituents, hybridization of the carbon atom, and solvent o n the properties of the complexes have been investigated. strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.