Hydrogen bonding and dipolar interactions between quinolines and organic solvents. Nuclear magnetic resonance and ultraviolet-visible spectroscopic studies

摘要

Solvatochromic studies on quinoline (Q), 3-cyanoquinoline (CNQ), 3-bromoquinoline (BrQ) and 8-hydroxyquinoline (OHQ) in pure solvents and alcohol-cyclohexane mixtures have been performed. The results are compared with Proton Nuclear Magnetic Resonance, H-1 NMR, studies and AMI calculations. Taft and Kamlet's solvatochromic comparison method was used to disclose solvent effects in pure solvents. These studies shows that the hydrogen bond acceptor ability of the Q ring is diminished and its polarity is increased by the presence of the cyano group in CNQ and the bromo group in BI Q. In OHQ, intramolecular hydrogen bonding has been observed. This interaction is weakened by the interaction with protic solvents. The studies ill binary mixtures, alcohol-cyclohexane, show solute-solvent interactions, which compete with solvent self-association in the preferential solvation phenomena. Alcohols with strong ability to self-associate have less preference toward solvation of these compounds. The association constants for solute-ethanol systems were determined by H-1 NMR. The results show that the solvent hydrogen bond donor ability is the main factor involved in the interaction with these solutes at the aza aromatic site. (C) 2001 Elsevier Science B.V. All lights reserved. [References: 52]