PARTITION COEFFICIENTS AND INTRAMOLECULAR HYDROGEN BONDING. 2. THE INFLUENCE OF PARTITION SOLVENTS ON THE INTRAMOLECULAR HYDROGEN-BOND STABILITY OF SALICYCLIC ACID DERIVATIVES

摘要

The intramolecular hydrogen bonding (chelation) of salicylaldehyde, methyl salicylate, N,N-dimethylsalicylamide and 2-hydroxyacetophenone was studied by IR spectroscopy in different phases used for partition coefficient determinations. The extent of chelation was found to be highly sensitive to the solvent and to the substituent on the carbonyl group in the orders carbon tetrachloride = chloroform > > octanol > water > > dimethyl sulfoxide and OMe ≈ Me > H > > NMe_2. These sequences are discussed in terms of hydrogen-bond acidity of the hydroxyl group, hydrogen-bond basicity of the carbonyl group, planarity of the solute molecule and hydrogen-bond acidity/basicity properties of the solvent. Semi-empirical and ab initio calculations confirmed the substituent sequence.