Hydrogen-bonding association model complexes

C3+ complex cation always favors the homochiral combination (A-A or A-A) with the complex anion, while the C2 " complex cation always favors the heterochiral combination (A-A or A-A) with the complex anion. This tendency is explained by assuming that straight N-H--0 hydrogen bonds are formed in such a favorable pair. This hydrogen bonding association model has made possible the highly efficient optical resolution of electrically neutral tris(aminoacidato)cobalt( III). 

It should be noted that the regular solution theory, upon which Eqs. (3.31) and (3.32) are based, is valid only for solute-solvent systems that are free of strong associative behavior, such as hydrogen bonding, solvation, or complex formation (Modell and Reid 1983). As such, Eq. (3.32) is correctly applied to ideal systems or nonideal systems that exhibit positive, as opposed to negative. 

Pyrrole also acts as a -electron donor in association with tri-halomethanes to form weak 1 1 CH-7T complexes (20).141 Similarly pyrrole appears to form (pyrrole) 7T-H-0 bonds with phenol instead of an NH-O hydrogen bond or NH-v (phenol) bonds.112 The association between pyrrole and nitriles has been described both as NH-N132 (21) and as NH-n-146,156 (22) hydrogen-bonded complexes. No definite conclusion has been reached but the NH frequency difference between the bonded and nonbonded vibration is more compatible with a NH-7r-bonded model (Table IV). 

The stability of a cyclic multimolecular aggregate stabilized by intermolecular interactions is not simply a consequence of AG°, since this thermodynamic variable does not take into account the effect of the concentration (entropy) on the extent of the aggregation. The concepts derived from the study of simple model systems of macrocyclic structures stabilized by hydrogen bonds could be used to rationalize the association of more complex biological aggregates. 

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