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

The intramolecular hydrogen bonding (chelation) of salicylaldehyde, me thyl salicylate, N,N-dimethylsalicylamide and 2-hydroxyacetophenone wa s studied by IR spectroscopy in different phases used for partition Co efficient determinations. The extent of chelation was found to be high ly sensitive to the solvent and to the substituent on the carbonyl gro up in the orders carbon tetrachloride = chloroform much greater than o ctanol > water much greater than dimethyl sulfoxide and OMe approximat e to Me > H much greater than NMe(2). These sequences are discussed in terms of hydrogen-bond acidity of the hydroxyl group, hydrogen-bond b asicity of the carbonyl group, planarity of the solute molecule and hy drogen-bond acidity/basicity properties of the solvent. Semi-empirical and ab initio calculations confirmed the substituent sequence.