Related Experiment Video
Updated: Jun 23, 2026

Chemical Modification of the Tryptophan Residue in a Recombinant Ca2+-ATPase N-domain for Studying Tryptophan-ANS FRET
Published on: October 9, 2021
How nitrogen modifies the nuclear magnetic shielding in tetraazanaphthalenes
Inmaculada García Cuesta1, José Sánchez Marín, Alfredo M J Sánchez de Merás
1Instituto de Ciencia Molecular, Universidad de Valencia, P.O. Box 22085, E-46071, Valencia, Spain. garciain@uv.es
Abstract:
Although for planar conjugated hydrocarbons the out-of-plane component of proton magnetic shielding is an unquestionable quantitative aromaticity indicator, the same is not true for tetraazanaphthalenes. As in these compounds the (core + sigma)-currents associated to the nitrogen nuclei diminish the perpendicular component of shielding, abnormal values of (1)H NMR sigma(zz) are obtained. Therefore, a consistent aromaticity measure must be based only on the pi-contribution to the out-of-plane component of proton magnetic shielding. Otherwise, the behavior of these compounds in presence of an external magnetic field parallels that of naphthalene, with the nitrogen nuclei contributing to the ring current in a comparable amount to carbon nuclei. The pi-current contribution to magnetic shielding represents 6-8% of the out-of-plane shielding for nitrogen and 9-12% for carbon.
Related Concept Videos
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
π Electron Effects on Chemical Shift: Overview
Diamagnetic Shielding of Nuclei: Local Diamagnetic Current
Other Nuclides: 31P, 19F, 15N NMR
While fluorine-19 and phosphorous-31 have high natural abundances (100%) and positive gyromagnetic ratios, nitrogen-15 has a low natural abundance and a negative gyromagnetic ratio. However, nitrogen-15 is still preferred over nitrogen-14 (which has a high...
NMR Spectroscopy Of Amines
NMR Spectroscopy of Benzene Derivatives

