Structural and spectroscopic studies of new o-, m- and p-nitrobenzyl esters of lasalocid acid

New o-, m- and p-nitrobenzyl esters of lasalocid (o-ELAS, m-ELAS and p-ELAS) have been synthesised and studied by X-ray, 1H, 13C NMR, FT-IR, UV-Vis, fluorescence as well as PM5 semiempirical methods. The crystal structure of o-ELAS is stabilized by three intramolecular hydrogen bonds in which the ketone is not engaged. The FT-IR spectra of o-ELAS, m-ELAS and p-ELAS in the chloroform and acetonitrile solutions indicate that in these solvents other structures are realized in which the ketone group is hydrogen bonded. In the solution the hydrogen bonds in which the carbonyl ester groups are involved becomes slightly weaker and partially dissociated. The dissociation of these hydrogen bonds increases with increasing solvent polarity. The structures of the o-, m- and p-nitrobenzyl esters of lasalocid acid are discussed in detail.