Diazanaphthalenes: A 13C NMR investigation on the site of protonation and pKa values

Peter van de Weijer, Hans Thijsse, Douwe van der Meer

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Abstract

The pH dependence of the 13C chemical shifts (δ) of the diazanaphthalenes has been recorded. From this dependence the pKa values have been determined using the Henderson-Hasselbach equation. The change in 13C chemical shifts under the influence of nitrogen protonation (Δδ) has been predicted using the Δδ values of quinoline and isoquinoline. The correlation between observed and expected Δδ values of the symmetric diazanaphthalenes is very good. Assuming these changes in chemical shifts to be of general validity, the site of protonation in the asymmetric diazanaphthalenes has been determined by comparison of the expected Δδ values for α- and ß-nitrogen protonation with the observed ones. The site of protonation for 1,6- and 1,7-naphthyridine is the ß-nitrogen atom, whereas for cinnoline both monoprotonated species are present in a significant amount.
Original languageUndefined
Pages (from-to)187-191
JournalOrganic Magnetic Resonance
Volume8
Issue number4
DOIs
Publication statusPublished - 1976
Externally publishedYes

Keywords

  • IR-70728

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