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13C NMR spectra of substituted pyridine N-oxides. Substituent and hydrogen bonding effects

✍ Scribed by B. Brycki; B. Nowak-Wydra; M. Szafran

Publisher: John Wiley and Sons
Year: 1988
Tongue: English
Weight: 282 KB
Volume: 26
Category: Article
ISSN: 0749-1581
DOI: 10.1002/mrc.1260260406

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✦ Synopsis

Aromatic I3C chemical shifts of 4-and hubstituted pyridine N-oxides in aprotic and protic solvents are reported and discussed. Changes in chemical shifts caused by hydrogen bonding and protonation are much smaller than those induced by a substituent, and are not related to the pK, values of N-oxides. Since the effect of hydrogen bonding is not in the same direction as that due to the substituent effect, the estimation of proton transfer from measured chemical shifts is not possible in complexes of pyridine N-oxides with trifluoroacetic acid. A linear correlation is obtained between the ips0 carbon substituent chemical shifts of 4-and %substituted pyridine N-oxides and monosubstituted benzenes, which supports the suggestion that electronic factors other than A,, are more important for the ips0 carbon.

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