Abstract
1H, 13C, and 15N NMR chemical shifts have been measured for 2-aminopyridine N-oxide (1), its eleven derivatives (2–10, 13, 14), and 3-Cl and 3-Br substituted 4-nitropyridine N-oxides (11, 12). δ(15N) of pyridine ring nitrogen in 2-acetylaminopyridine N-oxides are 5.9–11.5 ppm deshielded from those in 2-aminopyridine N-oxides. When amino and acetylamino substituents are in 4-position, δ(15N) of ring nitrogen is 21.3 ppm deshielded in the acetylated derivative. The strong resonance interaction between 2-amino and 5-nitro groups reflects in the decrease of amino nitrogen shielding about 5.3–17.9 ppm. Also, 1H and 13C NMR spectral data are in agreement with 15N NMR results reflected as deshielded amino protons and carbons C-2 and C-5. The pyridine nitrogen chemical shift in all amino- and acetylamino derivatives vary between −101.2 and −126.7 ppm, which has been connected with the tautomeric balance in our earlier studies.
Highlights
15N isotope is the most sensitive NMR nucleus to the effect of a substituent introduced to pyridine N-oxide (2- and 4-amino, 2- and 4-acetylamino, methyl group in different positions together with 2-amino and/or 2-acetylamino, 5-nitro with 2-amino, 4-nitro together with 3-chloro and 3-bromo e.g.)
When amino and acetylamino substituents are in 4-position, d(15N) of ring nitrogen is 21.3 ppm deshielded in the acetylated derivative
The strong resonance interaction between 2-amino and 5-nitro groups reflects in the decrease of amino nitrogen shielding about 5.3–17.9 ppm
Summary
Received: 6 February 2012 / Accepted: 15 May 2012 / Published online: 26 June 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com. D(15N) of pyridine ring nitrogen in 2-acetylaminopyridine N-oxides are 5.9–11.5 ppm deshielded from those in 2-aminopyridine N-oxides. When amino and acetylamino substituents are in 4-position, d(15N) of ring nitrogen is 21.3 ppm deshielded in the acetylated derivative. The pyridine nitrogen chemical shift in all amino- and acetylamino derivatives vary between -101.2 and -126.7 ppm, which has been connected with the tautomeric balance in our earlier studies. Talik Department of Bioorganic Chemistry, Faculty of Industry and Economics, University of Economics, 53-345 Wrocław, Poland. Kolehmainen Department of Chemistry, University of Jyvaskyla, FI-40014 Jyvaskyla, Finland
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