15N chemical shifts of a series of isatin oxime ethers and their corresponding nitrone isomers

• Published in: Magnetic resonance in chemistry 2010-11, Vol.48 (11), p.873-876
• Main Authors: Liu, Xiaohong, Huang, Xiaohua Stella, Sin, Ny, Venables, Brian L., Roongta, Vikram
• Format: Article
• Language: English
• Subjects: 15N chemical shifts; Alkylation; alkylation of oximes; Electrons; Ethers; Ethers - chemical synthesis; Ethers - chemistry; Isatin - analogs & derivatives; Isatin - chemical synthesis; Isatin - chemistry; Isomers; long-range HN coupling constant; Magnetic resonance; Magnetic Resonance Spectroscopy - standards; Molecular Structure; N-15 NMR; Nitrogen Isotopes; Nitrogen Oxides - chemical synthesis; Nitrogen Oxides - chemistry; nitrone; NMR; Nuclear magnetic resonance; oxime; Oximes; Oximes - chemical synthesis; Oximes - chemistry; Reaction products; Reference Standards; Stereoisomerism
• ISSN: 0749-1581; 1097-458X; 1097-458X
• DOI: 10.1002/mrc.2680

In this article, we describe the characteristic 15N chemical shifts of isatin oxime ethers and their isomer nitrone. These oxime ethers and nitrones are the alkylation reaction products of isatin oximes. In our study, the 15N chemical shifts observed in these oxime ethers were in the 402–408 (or 22–28) ppm range, although those for their corresponding nitrone series were in the 280–320 (or −100 to −60) ppm range. This remarkable difference in 15N NMR chemical shift values could potentially be used to determine the O‐ versus N‐alkylation of oximes, even when only one isomer is available. In this paper, the differences in 15N NMR chemical shifts serve as the basis for a discussion about how to distinguish both regioisomers derived from the oximes alkylation. Copyright © 2010 John Wiley & Sons, Ltd. Characteristic 15N chemical shifts for the isatin oxime ethers and their nitrones were observed. The chemical shift differences between nitrone and oxime ether are greater than 50 ppm so it could be applied to differentiate the O‐ versus N‐alkylation of oximes, even when only one isomer is available.