Abstract
AbstractThe 17O chemical shift data for a series of azine N‐oxides, diazine N‐oxides and di‐N‐oxides at natural abundance are reported. Isomeric methyl substituted quinoline N‐oxides exhibited chemical shifts which are interpreted in terms of electronic and compressional effects. The 17O chemical shift for 8‐methylquinoline N‐oxide (370 ppm) is deshielded by 25 ppm more than predicted, based upon electronic considerations. The 17O chemical shift for the N‐oxide of 8‐hydroxyquinoline (289 ppm) is substantially shielded as a result of intramolecular hydrogen bonding. The relative 17O chemical shifts for diazine N‐oxides of pyrazine, pyridazine and pyrimidine follow predictions based on back donation considerations. Because of solubility limitations, spectra of only two N,N′‐dioxides were obtained. The chemical shift of benzopyrazine di N‐oxide in acetonitrile was shielded by 18 ppm compared to that of its mono N‐oxide.
Published Version
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