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17O-NMR Spectra of Mesoionic Compounds: The polarized carbonyl group

1988; Wiley; Volume: 71; Issue: 1 Linguagem: Inglês

10.1002/hlca.19880710126

1522-2675

H. Dahn, My‐Ngoc Ung‐Truong,

Click Chemistry and Applications

Abstract The 17 O‐NMR spectra of 5 mesoionic compounds have been measured; in two cases, the peak attribution between endo‐ and exocyclic O‐atoms has been made unambiguous by synthesizing specifically O‐labelled samples. The signal of the exocyclic O‐atom appears at particularly high field, closer to the values of enolate than of carbonyl O‐atoms. The cyclic O‐atom resonates close to values of furans (or isoxazol, if bound to N). The exocyclic O‐atom is much more susceptible to structure and substituent variations than the endocyclic, an observation which is in favour of a chain‐conjugated (non‐aromatic) structure 1E .