Hydrogen Bonding and Solvent Polarity Effects on the Nitrogen NMR Shielding of 1,2,4,5-Tetrazine

A Study of Solvent Polarity and Hydrogen Bonding Effects on the Nitrogen NMR Shielding of Isomeric Tetrazoles andab InitioCalculation of the Nitrogen Shielding of Azole Systems

“…These are represented by the least-squares fitted values of the a term in Eq. [1] as reported triazines, and 1,2,4,5-tetrazine (1)(2)(3)(4)(5)(6)(7)(8). This is also in accord with analogous effects found in other molecular systems where in Table 3.…”

“…We have already shown that the a terms obtained for pyridinetype nitrogen shieldings of azine heteroaromatics (6-8) and for triazole ring systems (3) provide a sensitive probe for relative affinities of these nitrogens as acceptors of hydrogen bonds; the latter affinities may be termed an exhibition of variations in ''soft'' basicity, while analogous affinities with respect to a complete proton transfer should then be termed ''hard'' basicity. We have also found indications that the affinity of the nitrogen atoms concerned to accepting hydrogen bonds from solvent molecules, measured by the a terms for the relevant nitrogen shieldings, parallels that with respect to gas-phase protonation, as reckoned from ab initio calculated protonation energies (3,(6)(7)(8). The tetrazole systems examined in the present work should provide a rigorous test for such a correlation, in view of the fact that each contains three nonequivalent pyridine-type nitrogen atoms which can enter com- petition with respect to hydrogen bond or proton acceptance.…”

Solvent Effects on Oxygen-17 Chemical Shifts in Methyl Formate: Linear Solvation Shift Relationships

“…The application of the KAT formalism to the analysis of the solvent effects on 17 O chemical shifts is scarce (4,15). On the contrary, the application of this formalism to the chemical shifts of the other nuclei ( 1 H, 13 C, 19 F, . .…”

Solution‐phase chemical shift anisotropy as a promising tool to probe intermolecular interactions and peptide bond geometry: a case study on 15N‐labeled Nα‐t‐Boc‐L‐valine

“…The change of the CSA caused by the difference in the amide-solvent interactions has contributions from the through-space shielding effect of the neighboring solvent molecules and also from the bond polarization effect of the intermolecular interactions. 7,45,46 As shown in Table 2, the observed range of the solvent-induced variation of 15 using the known effective correlation times and assuming an axial symmetry of the chemical shift tensors.…”