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Diazanaphthalenes: A 13 C NMR investigation on the site of protonation and p K a values
Author(s) -
van de Weijer Peter,
Thijsse Hans,
van der Meer Douwe
Publication year - 1976
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270080406
Subject(s) - protonation , chemistry , chemical shift , isoquinoline , nitrogen , quinoline , cinnoline , nitrogen atom , proton , a value , computational chemistry , stereochemistry , medicinal chemistry , organic chemistry , group (periodic table) , ion , physics , quantum mechanics
Abstract The pH dependence of the 13 C chemical shifts (δ) of the diazanaphthalenes has been recorded. From this dependence the p K a values have been determined using the Henderson‐Hasselbach equation. The change in 13 C 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 β‐nitrogen protonation with the observed ones. The site of protonation for 1,6‐ and 1,7‐naphthyridine is the β‐nitrogen atom, whereas for cinnoline both monoprotonated species are present in a significant amount.