Dicarbonyls, Group structural properties

PHYSICAL, SPECTROSCOPIC, AND STRUCTURAL PROPERTIES OF THE VARIOUS GROUP 4B METALLOCENE DICARBONYLS... 

Structure.—Tautomerism. The tautomeric properties of monothio-/3-dicarbonyl compounds have been extensively studied by several groups of workers in the past two years, and notable progress has been made. In order to clarify the direction of tautomerization in thioacetylacetone (505 R = R = Me, R = H), Fabian compared the experimental u.v. spectrum of this compound with those derived theoretically for each of the tautomeric forms (504)—(506), and he was able to conclude that thioacetylacetone exists in solution as an equilibrium mixture of the two rapidly interconvertible forms (504) and (506) [in cyclohexane -70% (506)]. j3-Thioxo-aldehydes (505 R = Ar, R = Me or Ar, R = H) appeared to exist in solution as an equilibrium mixture of the two rapidly interconvertible forms (504) and (506), together with the trans-enethiol form (507). Rather surprisingly, a-alkyl monothiodibenzoylmethanes (505 R = R = Ph, R = alkyl) turned out to exist in solution as mixtures of the trans-enethiol tautomer (507) and the trans-enol tautomer (508). The existence of the forms (507) and (508) is doubtless a consequence of... 

---