Temperature-induced reversal of proton tautomerism: role of hydrogen bonding and aggregation in 7-hydroxyquinolines.
UV-vis absorption spectra of 7-hydroxyquinolines in saturated hydrocarbon solvents were measured at various temperatures between 293 and 77 K. The tautomeric equilibrium was found to reverse when the temperature was lowered. At 293 K, the enol form was exclusively present. As the temperature was lowered, the enol form decreased substantially, and the keto form became predominant. A close examination of the spectral changes suggests that the reversal of the tautomeric equilibrium at lower temperatures proceeds in two steps: aggregation of the enol forms by intermolecular hydrogen bonding and further aggregation of the hydrogen-bonded aggregates.
Miura
Masatoshi
M
Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Harada
Jun
J
Ogawa
Keiichiro
K
D002627:Chemistry, Physical / Q000379:methods; D004247:DNA / Q000737:chemistry; D006860:Hydrogen Bonding; D006912:Hydroxyquinolines / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D011522:Protons; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013696:Temperature