Structural and spectroscopic studies of a new 2-naphthylmethyl ester of lasalocid acid

A new lasalocid 2-naphthylmethyl ester (NAFB) has been synthesised and studied by X-ray, 1H NMR, 13C NMR, FT-IR, UV–vis, fluorescence-spectroscopy as well as by the PM5 semiempirical method. The crystals of NAFB are monoclinic, space group P21 with a = 10.120(2) Å, b = 18.245(3) Å, c = 12.354(3) Å, β = 109.65(3)˚ and Z = 2. The molecular conformation of NAFB in the solid state is stabilized by three intramolecular hydrogen bonds, and no intermolecular H-bonds are formed. The FT-IR spectrum of NAFB in chloroform indicates equilibrium between two NAFB conformers. In the first conformer the keto group forms an intramolecular hydrogen bond, while in the second one this group is not involved in any hydrogen bonds. The two structures of NAFB are calculated by the PM5 method and discussed in detail.