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

In this article, we describe the characteristic 15 N 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 15 N 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 15 N 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 15 N 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.