Chiroptical and conformational properties of (R)-1-phenylethylamine derivatives of persubstituted benzene

Chiral derivatives of 2,4,5,6-tetrachloro-1,3-dicyanobenzene 1 with one, two and three (R)-1-phenylethylamino ((R)-PEA) units 2–4 are prepared and their chiroptical and conformational properties discussed on the bases of the UV/CD, NMR and MM2 data. High polarity of the persubstituted benzene ring leads to peculiar UV and IR spectra of achiral model compounds 5–7, whereas relatively rigid conformations of the chiral analogues 2–4 are reflected in the CD spectra. Strong exciton coupling (EC) appears in the CD spectrum of pseudo-C₃-symmetric 4; this type of interaction seems not to be present in the C₁-symmetric 2 and C₂-symmetric 3. The absence of a molecular cleft in the chiral structures 2–4 could explain their inability to recognise the enantiomers of some racemates in the NMR experiment.