| Abstract: | Whereas tropone ( 2 ) and a cyclopropanone 5 show rather normal ketone signals in their 17O-NMR spectra, the two cyclopropenones 1a , and lb exhibit exceptionally high shielding, indicating a structure closer to a ? O? formula than to a ketone. For comparison, an enolate and several phenolates have been measured. In order to test the ketonic character, the nucleophilic addition of water was determined by the rate of isotopic O-exchange between ketone and water: 2 exchanged ca. 20 times slower than acetophenone, whereas la reacted very much more slowly. |
