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Theoretical and experimental study of 15 N NMR protonation shifts
Author(s) -
Semenov Valentin A.,
Samultsev Dmitry O.,
Krivdin Leonid B.
Publication year - 2015
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4231
Subject(s) - protonation , chemistry , chemical shift , lone pair , supermolecule , nitrogen , computational chemistry , solvation , solvent effects , solvent , crystallography , molecule , organic chemistry , ion
A combined theoretical and experimental study revealed that the nature of the upfield (shielding) protonation effect in 15 N NMR originates in the change of the contribution of the sp 2 ‐hybridized nitrogen lone pair on protonation resulting in a marked shielding of nitrogen of about 100 ppm. On the contrary, for amine‐type nitrogen, protonation of the nitrogen lone pair results in the deshielding protonation effect of about 25 ppm, so that the total deshielding protonation effect of about 10 ppm is due to the interplay of the contributions of adjacent natural bond orbitals. A versatile computational scheme for the calculation of 15 N NMR chemical shifts of protonated nitrogen species and their neutral precursors is proposed at the density functional theory level taking into account solvent effects within the supermolecule solvation model. Copyright © 2015 John Wiley & Sons, Ltd.