Partition coefficients and intramolecular hydrogen bonding. 1. The hydrogen-bond basicity of intramolecular hydrogen-bonded heteroatoms

✍ Scribed by Michel Berthelot; Christian Laurence; Denis Foucher; Robert W. Taft

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 478 KB
• Volume: 9
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199605)9:5<255::aid-poc779>3.0.co;2-g

✦ Synopsis

Measurements were made in CCI, of the formation constant K,, of the 1 : l hydrogen-bonded complexes between the reference donor 4-fluorophenol and the intramolecular hydrogen-bonded systems I (one lone pair on heteroatom Y, one intramolecular hydrogen bond: 8-hydroxyquinaldine and 2-(2-hydroxyphenyl) benzoxazole); JI: (two lone pairs, two intramolecular hydrogen bonds: 2,2'-dihydroxybenzophenone and 1,8dihydroxyanthrone) and Ill (two lone pairs, one intramolecular hydrogen bond: tropolone, salicylic acid derivatives and guaiacol). The pK,, values and the structural vibrational studies show that system I has a nonzero hydrogen-bond basicity which is due to the oxygen atom. In system 11 the non-zero basicity is explained by the two oxygens and the breaking of one intramolecular hydrogen bond. In the push-pull system III (e.g. tropolone), in spite of the great decrease of the basicity of the free lone pair by the intramolecular hydrogen bond (e.g. compared with tropone), Y remains the major site for intermolecular association. However in guaiacol, a non push-pull system Ill, the cooperativity effect makes the phenolic oxygen the major site.