15N NMR Applications

Linking the Character of the Metal–Ligand Bond to the Ligand NMR Shielding in Transition-Metal Complexes: NMR Contributions from Spin–Orbit Coupling

“…There are two types of occupied σ-bonding MOs with significant contributions to σ p (N) shown in Figure : σ N–C (MO55 for 1a , MO54 for 1i ) and σ Au–N (MO54 for 1a , MO55 for 1i ). They are both magnetically coupled to the vacant π-type MO*s with sizable nitrogen 2p y AOs character. , The schematic representation of the σ Au–N ↔π* coupling is shown as the Ramsey-type paramagnetic contribution in Figure a. As the trans substituent X efficiently alters the energy of the Au–N bond, the role of the σ Au–N -type orbitals in σ p contributions varies significantly in the series of compounds.…”

“…The diamagnetic contribution reflects the total ground-state electron density around the NMR spectator atom and is relatively invariant to the change in its chemical environment. In contrast, the paramagnetic contribution originates in couplings between the occupied and vacant frontier molecular orbitals (MOs) in the presence of magnetic field and provides important chemical information about the molecular electronic structure and bonding. , In the following, we focus on the NMR shielding constants of light ligand atoms (L) in compounds containing heavy atoms (HA) where relativistic effects, which originate at the HA and propagate to the neighboring L, play a significant role. − The relativistic contribution to the NMR shielding constant of L is typically heavily modulated by the spin–orbit (SO) coupling term (σ SO ): − The σ SO can be obtained as a perturbation to nonrelativistic or scalar-relativistic one-component (1c) calculations. − Traditionally, these 1c approaches are used in chemistry to establish a link between the electronic molecular structure and the shielding mechanism for individual atoms. In calculations of NMR shielding constant using variational treatment of relativistic effects, such as two-component (2c) SO-ZORA or four-component (4c) DKS approaches used in this work, the σ is naturally relativistic.…”

Structure, solvent, and relativistic effects on the NMR chemical shifts in square-planar transition-metal complexes: assessment of DFT approaches

“…The increased EE admixture improves the results for some cases already in vacuo, particularly for 13 C NMR CS, where the solvent effects obviously play a less significant role compared to 15 N NMR CS. 80,[83][84][85] For instance, the PBE functional results in Dd( 13 C) = 21.4 ppm for Pt1-C, whereas PBE-40 gives Dd( 13 C) = 1.5 ppm (see Fig. 6).…”

An investigation of the predominant structure of antibiotic azithromycin in chloroform solution through NMR and thermodynamic analysis

“…The 15 N NMR can provide valuable information about the electronic structure of molecular systems, orientation, and tautomerism, in addition to being one of the main techniques for studying the structure of heterocycles. 47,48 In the present study, the 15 N shielding constant ( σ 15 N) was calculated at the DFT level employing two computational protocols: using the B3LYP functional with 6-31G(d,p) basis set 39 (named B3LYP/6-31G(d,p)-IEF-PCM(UFF)), and with the meta-GGA TPSS functional, 49 using the pcSseg-2 basis sets 50 (named TPSS/pcSseg-2). The solvent effects (chloroform) were considered through the IEF-PCM(UFF) model and adding explicit solvent molecules.…”