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13 C and 15 N NMR studies of 1,2‐benzisoxazole 2‐oxides, 1,2‐benzisoxazoles and 2‐hydroxyaryl ketoximes
Author(s) -
Tsoungas Petros G.,
De Costa Bruce F.
Publication year - 1988
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.1260260104
Subject(s) - chemistry , isoxazole , chemical shift , resonance (particle physics) , medicinal chemistry , stereochemistry , nuclear chemistry , physics , particle physics
13 C and 15 N chemical shift assignments of a number of 1,2‐benzisoxazole 2‐oxides and their deoxygenated analogues are reported and discussed. Similarly, assignments for some of the precursors to the N ‐oxides, o ‐hydroxyaryl ketoximes, are reported. In the N ‐oxides the “push‐pull” effect of the NO dipole is largely localized on the isoxazole unit. A large ( ca 39 ppm) upfield shift of the C‐3 resonance is caused by the exocyclic oxygen whereas C‐7a and, to a lesser extent, C‐6 are the most heavily deshielded nuclei. The substituents do not have a significant effect on the C‐3 resonance, whereas their effect on the carbocyclic carbons is more pronounced, the most markedly affected being the C‐4 and C‐6 nuclei. N ‐Oxidation of 1,2‐benzisoxazole causes a large (50.5 ppm) shielding of the 15 N nucleus.