Multinuclear magnetic resonance study of tautomerism in fluorinated β-diketones

✍ Scribed by S. R. Salman; R. D. Farrant; J. C. Lindon

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 613 KB
• Volume: 28
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260280716

✦ Synopsis

Abstract

Multinuclear NMR experiments on fluorinated β‐diketones have furnished information on the various tautomers present in solution and their proportions. 2‐Trifluoroacetyl‐1‐indalone in CDCI~3~ solution exists in the enol form, as a mixture of exocyclic and endocyclic cis‐enols with the exocyclic form favoured, but in DMF‐d~7~ solution the equilibrium shifts to 40% enol, 60% hydrate with the enol and hydrate being in slow exchange on the NMR time scale. 2‐Trifluoroacetyl‐1‐tetralone in CDCI~3~ solution exists only as the enol forms, approximately equally populated, but in DMF‐d~7~, unlike the indalone, no hydrate is formed although there is now 6% of the keto form present in slow exchange. The experimental results were compared with calculated data produced using molecular orbital simulations. These agree with the NMR results and predict that the tetralone enol tautomers are both significantly populated at room temperature but that the indalone exists primarily as the exocyclic enol. The oxygen‐oxygen internuclear distance in the hydrogen bond was estimated from the OH proton chemical shift based on a calibration from solid‐state data from model compounds, and agrees well with the predictions using the molecular mechanics approach.