Journal of the Chemical Society. Perkin transactions II p. 1768 - 1773 (1980)
Update date:2022-07-29
Topics:
Carlsen, Lars
Duus, Fritz
Aromatic β-thioketones exist in solution as mixture of rapidly interconverting Z-enol and Z-enethiol tautomers.The electronic absorption spectra exhibit in general four absorption bands in the u.v.-visible region at ca. 265 (ArC=O ?,?*; ArC=C ?,?*), 330 (ArC=S ?,?*; O=CC=CS ?,?*; C=O n,?*), 415 (OC=CC=CS ?,Π*), and 520 nm (C=S n,Π*), respectively.The β-thioxoketones are converted by sodium hydroxide into the corresponding anions.CNDO/B Calculations predict that the negative charge in the β-thioxoketonates is delocalized over the OCCCS system, suggesting simultaneously sickles or W shaped conformations.Two characteristic absorption bands found for the β-thioxoketonates at ca. 275 and 400 nm are assigned to ?,?* transitions involving the Ar-C<*>C<*>C-Ar' and S<*>C<*>C<*>C<*>O chromophores, respectively.The enol-enethiol tautomeric equilibrium has been studied by means of low temperature spectroscopy.At room temperature equilibrium constants (K293) of 3-5 have been found corresponding to a 4:1 enol-enethiol concentration ratio.The reaction entropy (ΔSr) has been found to be negative for the enethiol->enol conversion,reflecting the intramolecular O-H...S hydrogen bonds to be considerably stronger than the corresponding O...H-S hydrogen bond.Variation in ΔSr and K293 as functions of substitution in the aryl group next to oxygen are discussed.
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