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NMR of terminal oxygen. 15 17 O NMR spectra of the N + O − group: tert ‐Amine oxides R 3 N + O − , nitrones HC N + (O − ), azoxy derivatives N N + (O − ), nitrile oxides C N + O − and related compounds. Shielding anisotropy in linear heteroatomar π‐systems
Author(s) -
Dahn Hans,
Péchy Péter,
Van Toan Vien,
Carrupt PierreAlain
Publication year - 1995
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260330408
Subject(s) - chemistry , azoxy , nmr spectra database , resonance (particle physics) , crystallography , amine gas treating , protonation , nitroso , nuclear magnetic resonance spectroscopy , nitroso compounds , stereochemistry , spectral line , medicinal chemistry , organic chemistry , particle physics , astronomy , ion , physics
The 17 O 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. XN + (O − )Ar compounds (X =; R 2 C, nitrones; X = RN, azoxy compounds; X = ArN(O), azodioxy compounds = C ‐nitroso dimers) are more deshielded, δ o 350–450 ppm, due to resonance participation of NOtype structures (true nitroso compounds XNO appear at 650–1500 ppm). Carbonitrile oxides RCN + O − and NN + O − show high shielding, δ o 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 sp 2 ‐type π‐systems, is explained by the shielding anisotropy in linear (sp‐type) π‐systems. The shift values observed for four classes of NO compounds are in excellent agreement with predictions by IGLO calculations.