Density functional study of stereo-chemistry and chiroptics of helical alkynyl cyclophanes with binaphthyls

Stereo-chemistry and chiroptics of several alkynyl cyclophanes with multiple binaphthyls are investigated using density functional calculations. It is revealed that the lower-energy Cotton effects of tetragon-shape cyclophanes originate from electronic transitions on two long sides while the higher-energy Cotton effects have important origin in electronic transitions on two short sides. According to spectral characteristic and relative energy, we deduce that two low-energy conformers of S5 with two meta-position-substituted benzene rings are likely to coexist. For S6 as a macrocyclic molecule including eight binaphthyls, we infer that only one conformer as S6c is populated. This conformer is of a groove-shape structure with the αβαβ orientation of four meta-position-substituted benzene rings.

Stereo-chemistry and chiroptics of several alkynyl cyclophanes with multiple binaphthyls are investigated using density functional calculations.Figure optionsDownload as PowerPoint slideHighlights
► The ECD spectra depend on the rotational dihedral angle between two naphthyl planes.
► The ECD spectra come from electronic transitions of long edges or short edges.
► For S5, the two lowest-energy conformers are likely to coexist.
► For S6, only one conformer is likely to be populated.