FORMATION OF 3-MEMBERED AND 4-MEMBERED-RING STRUCTURES FOR THE LI+ ADDUCTS OF APPROPRIATE AZINES

Wide deviations (enhanced stabilities) from a linear relationship between the corresponding stability constants (given as Gibbs standard free energies of complexing) for gaseous Li+ and H+ adducts of monodentate diazines and pyridines are found for pyridazine, 2-fluoropyridine, and 1,8-naphthyridine. These results are interpreted to indicate the formation of a bidentate ring structure for the latter three compounds (and others of similar structures) with Li+ but not with H+. Ab initio calculations of structures and energies show the most stable forms of all of the H+ adducts to be monodentate, whereas three and four-membered-ring bidentate structures are confirmed for the Li+ adducts of the three above-mentioned compounds. The charge distributions obtained support the previous conclusion that bonding to H+ is largely covalent, whereas that to Li+ is largely ionic. © 1990, American Chemical Society. All rights reserved.