Spectroscopic and PM5 studies of a new Schiff base of Gossypol with 4′-aminobenzo-15-crown-5 in solution

The Schiff base of racemic gossypol with 4′-aminobenzo-15-crown-5 (GSABC) has been synthesised and studied by FT-IR, 1H and 13C NMR spectroscopy as well as by the PM5 semiempirical method. The spectroscopic methods have provided clear evidence that GSABC exists in solution in the enamine-enamine tautomeric form. The structure of GSABC and the hydrogen bonds within this structure are discussed. Additionally, the aromatic rings from gossypol and benzocrown parts are mutually coplanar, which affects the strength of the hydrogen bonds within the molecular structure and the conjugation between these two parts.