Abstract
The conformational state of two benzo-crown ethers with substantially different physiological activity, 2,3-(4′-phenylacetyl)- and 2,3-(4′-diphenylacetyl)benzo-15-crown-5, was studied in crystals and solutions in CH3CN and CCl4 by x-ray crystallographic analysis, IR spectroscopy, and conformational calculations by the method of molecular mechanics. Transition from the crystalline state to solutions was found to be accompanied by a substantial change in the conformation of the macrocyclic ring of all the compounds studied. The nature of the substituent in the benzene ring and the polarity of the solvent have an influence on the conformational state of the macrocyclic ring of the free ligand, which, however, is not the determining factor in the change in the activity of the compounds. The COCCOC fragments of the macrocyclic framework are conformationally labile, readily passing from gauche to trans conformations and the reverse, which is promoted by the negligible energy barriers between the different conformations, determined in the work by a molecular mechanics method.
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