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17O-NMR Spectra of Cyclopropenones and Tropone. Oxygen Exchange with Water

✍ Scribed by Hans Dahn; My-Ngoc Ung-Truong

Publisher: John Wiley and Sons
Year: 1987
Tongue: German
Weight: 441 KB
Volume: 70
Category: Article
ISSN: 0018-019X
DOI: 10.1002/hlca.19870700818

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✦ Synopsis

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Whereas tropone (2) and a cyclopropanone 5 show rather normal ketone signals in their "0-NMR spectra, the two cyclopropenones la, and l b exhibit exceptionally high shielding, indicating a structure closer to a -0formula 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 0-exchange between ketone and water; 2 exchanged ca. 20 times slower than acetophenone, whereas l a reacted very much more slowly. I ) 'The difficulty lies, of course, in thc selection of the proper reference compounds' [14]. ' )

Taking into account the deshielding influence of the N-atom, estimated at cu. 100 pprn [24], these N+-Ocompounds arrive at a 8, corresponding to that of cyclopropenone.

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