Comments on some chemical properties of diphenyl disulfide and its derivatives: II.Correlating the studies of reductive cleavage of disulfide bonds with the studies of anti‐human immunodeficiency virus activity with lowest unoccupied molecular orbital properties

The higher anti‐human immunodeficiency virus activity of a symmetrical 2,2′‐disubstitued derivative of diphenyl disulfide (DPDS) has been explained by the lower energy of the lowest unoccupied molecular orbital (LUMO), resulted from a better hydrogen bond stabilization of the σ*SS bond orbital (BO). This conclusion entails the participation of σ*SS BO in constructing the LUMO. The higher content of σ*SS BO, compared to π*CC BOs of phenyl groups, in LUMO of DPDS has been found through analysis of the LUMO of DPDS expanded in the BO space. The high content of σ*SS BO (%σ*SS) in the LUMO of DPDS has laid the foundation for the formation of σ‐type radical anion intermediate in the stepwise reductive cleavage of disulfide bond in the symmetrical 4,4′‐disubstitued DPDS derivatives. For the nine 4,4′‐disubstituted DPDS‐derivatives under reductive cleavage studies, the increasing %σ*SS in the LUMOs is parallel to the increasing value of inner reorganization energy. The unpaired electron accommodated by the lowest unoccupied molecular orbital of diphenyl disulfide (DPDS) is distributed more possibly on σ*SS BO than on π*CC bond orbitals of phenyl groups. This lays the foundation of formation of σ‐type radial anion of DPDS in the reductive cleavage mechanism