Formation of three- and four-membered-ring structures for the lithium(1+) adducts of appropriate azines

Abstract

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 Jbnaphthyridine. 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 threeand 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.

Absolute Binding Energies of Lithium Ions to Short Chain Alcohols, CnH2n+2O, n = 1−4, Determined by Threshold Collision-Induced Dissociation

“…The Li + affinities calculated at the semiempirical level of theory are significantly lower than the experimentally determined values. This appears to be largely because Li + retains about 0.8-0.9 of its charge in its adducts, 43 whereas the PM3 calculations indicate that only 0.7-0.8 of the positive charge is retained by Li + . The decreased charge retention by Li + in the calculated structures leads to longer Li + -O bond distances, which ranged from 2.07 to 2.12 Å in the Li + (ROH) complexes.…”

Gas-Phase Cation Basicities for Sulfuryl Species from Calculation and Experiment

“…Metal Ion Chelates. Compounds capable of chelating lithium are generally observed as outliers in LCB vs GB linear free energy relationships, since chelation can result in approximately 5−10 kcal/mol of stabilization energy over linear complexes. ,, Surprisingly, in this work, chelation of lithium and sodium by sulfuryl species was found to provide no special stabilization over linear complexation. Structures for lithium chelates were obtained at all levels of calculation for sulfone 1 and sulfate 9 , but no chelates were located for compounds containing the −O−SO fragment (e.g., 6 ).…”

“…Taft and co-workers' studies of nitrogen bases identified lithium chelates (e.g. of pyridazine) lying 6−8 kcal/mol above the LCB vs GB LFER . MO calculations on the sulfuryl species are in accord with the good correlation between LCB and GB across the series of sulfuryl species (Figure ) and are contraindicative of significantly stabilized lithium chelates.…”

“…A widening range of experimental techniques including Fourier transform ion cyclotron resonance spectroscopy (FT-ICR) allows measurements of basicities and affinities for cations in the gas phase. − Interest in these measurements lies, in part, in testing the physical methods themselves. − However, comparison of the gas-phase basicity of molecules toward cations provides fundamental information on intermolecular forces. In addition, gas-phase properties, such as gas-phase Brønsted basicity (GB), lithium cation basicity (LCB), and proton affinity (PA), provide (a) a starting point for theoretical approaches to solution phase properties (e.g., p K a ) and (b) an important means of testing newer molecular orbital (MO) and density functional theory (DFT) computational methods.…”

NMR studies of benzoannulation in lithium, sodium and potassium ortho-formylphenolates

“…Formation of the polymers by organolithium compounds [23][24][25] as well as by lithium phenolates [26] is a very common phenomenon. Different character of the sigma bonds formed between base and proton (polar covalent) and alkali metal cations (largely ionic) [27][28][29][30][31][32][33][34] are believed to be responsible for the differences observed in chelation of these species. As this can be seen (vide infera), the hitherto efforts were ineffective to show unequivocally the character of metal-oxygen interactions in lithium, sodium and potassium ortho-formyl(benzo)phenolates.…”