title: Theoretical and experimental study of 15N NMR protonation shifts.
abstract: A combined theoretical and experimental study revealed that the nature of the upfield (shielding) protonation effect in 15N 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 15N 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.
authors.affiliation: A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, Irkutsk, Irkutsk Oblast, 664033, Russia.
authors.forename: Valentin A
authors.initials: VA
authors.lastname: Semenov
authors.affiliation: A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, Irkutsk, Irkutsk Oblast, 664033, Russia.
authors.forename: Dmitry O
authors.initials: DO
authors.lastname: Samultsev
authors.affiliation: A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, Irkutsk, Irkutsk Oblast, 664033, Russia.
authors.forename: Leonid B
authors.initials: LB
authors.lastname: Krivdin
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D009587:Nitrogen Isotopes; D011522:Protons; D011789:Quantum Theory; D012015:Reference Standards
chemical_list: D009587:Nitrogen Isotopes; D011522:Protons
keywords: 15N NMR; GIAO-DFT; KT3; N-methylimidazole; absolute shielding constant; acetone oxime; chemical shift; pcS-3; protonation shifts; pyridine; triethylamine