ISSN:
0749-1581
Keywords:
17O NMR
;
tert-Amine oxides
;
Nitrones
;
Azoxy compounds
;
Azodioxy compounds
;
Nitrile oxides
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The 17O NMR signals of trimethylamine oxide and of six (para-substituted) N-aryldimethylamine oxides appear at 240-260 ppm, ca. 200 ppm more deshielded than hydroxylamines. The influence of the arene group and its substituents is small, confirming the absence of resonance interaction between the ring and the N+O- group. X=N+(O-)Ar compounds (X =; R2C, nitrones; X = RN, azoxy compounds; X = ArN(O), azodioxy compounds = C-nitroso dimers) are more deshielded, δo 350-450 ppm, due to resonance participation of —N=O—type structures (true nitroso compounds X—N=O appear at 650-1500 ppm). Carbonitrile oxides R—C≡N+—O- and N≡N+—O- show high shielding, δo ca. 140 and 115 ppm respectively, higher than amine oxides; their C and N atoms also are significantly shielded. The increase in shielding, relative to sp2-type π-systems, is explained by the shielding anisotropy in linear (sp-type) π-systems. The shift values observed for four classes of N—O compounds are in excellent agreement with predictions by IGLO calculations.
Additional Material:
5 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260330408
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