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17 O‐NMR Spectra of Mesoionic Compounds: The polarized carbonyl group
Author(s) -
Dahn Hans,
UngTruong MyNgoc
Publication year - 1988
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19880710126
Subject(s) - mesoionic , chemistry , substituent , carbonyl group , atom (system on chip) , conjugated system , group (periodic table) , nmr spectra database , spectral line , stereochemistry , carbon atom , crystallography , proton nmr , medicinal chemistry , ring (chemistry) , organic chemistry , physics , astronomy , computer science , embedded system , polymer
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 .