Multinuclear 1H, 13C and 15N NMR study of some substituted 2-amino-4-nitropyridines and their N-oxides.
1H, 13C and 15N NMR chemical shift assignments based on pulsed field gradient selected PFG 1H,X (X = 15C and 15N) HMQC and HMBC experiments are reported for three 4-nitropyridine N-oxides and four 4-nitropyridines. It was found that an ortho effect of a methyl group inhibits the deshielding effect of the 4-nitro group and that this effect and the so-called back donation is influenced by electronegativity and position of substituents in the multisubstituted pyridine N-oxides. The shielding effect of N-oxide group is most pronounced in the 15N NMR chemical shifts of the studied compounds. This effect is further modified by methylamino, methylnitramino, 5- or 3-methyl and 4-nitro groups. Among them the 4-nitro group exerts the highest influence on the shielding effect of the N-oxide functionality. Experimental 1H, 13C and 15N NMR chemical shifts and GIAO/DFT theoretical calculations are consistent with each other and supported by the reactivity on nucleophilic substitution, the UV spectral and the dipole moment data.
Laihia
K
K
Department of Chemistry, University of Jyväskylä, Finland. laihia@cc.jyu.fi
Kolehmainen
E
E
Kauppinen
R
R
Lorenc
J
J
Puszko
A
A
D002244:Carbon / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D009584:Nitrogen / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism*; D011725:Pyridines / Q000737:chemistry*; D014466:Ultraviolet Rays
D011725:Pyridines; C052728:4-nitropyridine; D002244:Carbon; D009584:Nitrogen; D010100:Oxygen