Observation by UV—Visible and NMR Spectroscopy and Theoretical Confirmation of 4-Isopropyltropolonate Ion, 4-Isopropyltropolone (Hinokitiol), and Protonated 4-Isopropyltropolone in Acetonitrile

摘要

Protonated 4-isopropyltropolone (H2L~+) was produced by the addition of methanesulfonic or trifluo-romethanesulfonic acid to 4-isopropyltropolone (hinokitiol: HL) dissolved in a protophobic aprotic solvent, acetonitrile, with poor solvation of anions and cations. The formation was confirmed by UV-visible and ~(13)C NMR spectroscopy as well as theoretical calculations using the Gaussian03 quantum chemistry package. The ~(13)C chemical shifts of all C-atoms in the seven-membered ring were properly assigned for H2L~+ and HL as well as for the deprotonated species, L~-. The influence of residual water in the organic solvent was regarded as negligible because such a water is in the "dihydrogen ether" condition.