Intermolecular shielding from molecular magnetic susceptibility. A new view of intermolecular ring current effects

Abstract

This paper presents calculations of the NICS (nuclear independent chemical shieldings) in a rectangular grid surrounding the molecules of benzene, naphthalene and coronene. Using the relationship between calculated NICS and the induced magnetic field, the calculated NICS are used to predict intermolecular effects due to molecular magnetic susceptibility or ring current effects. As expected from approximate ring current models, these intermolecular shielding effects are concentrated along the direction perpendicular to the molecular plane and they approach asymptotically to a dipolar functional dependence, i.e. (1-3 cos(2)theta)/r(3)). The deviations from the dipolar functional form require that the calculations of these intermolecular effects be done using a suitable interpolation scheme of the NICS calculated on the grid. The analysis of the NICS tensor components shows that these intermolecular shielding effects should be primarily expected on shielding components of the neighboring molecules nuclei, which are perpendicular to the molecular plane of the aromatic compound generating the induced field. The analysis of the calculated NICS along the series benzene, naphthalene and coronene shows that these intermolecular effects increase monotonically with the number of aromatic rings.

Intermolecular shielding contributions studied by modeling the C13 chemical-shift tensors of organic single crystals with plane waves

“…Induced current density on neighboring molecules can also directly contribute to the overall shift of the resonance frequency of the nucleus. 53 Although the chemical shift is domi- GAUSSVIEW͒ to the C 2 nucleus is color mapped onto the isosurface. The magnitude of the shielding is indicated by color ͑blue deshielding and red shielding͒, which ranges from Ϫ0.05 to 0.05 ppm.…”

Lattice simulation method to model diffusion and NMR spectra in porous materials

“…It is possible to calculate Nucleus Independent Chemical Shifts (NICS) for aromatic molecules using Density Functional Theory (DFT) calculations. 8,[11][12][13] These studies provide important insights, accounting, for example, for the shift to lower frequencies of NMR resonances of ions confined in a porous graphitic matrix. However, in order to arrive at a model that can describe all features of the experimental NMR spectra, the effects of local fluid structure and the ionic dynamics must be taken into account.…”

13C chemical-shift anisotropy of alkyl-substituted aromatic carbon in anthracene derivatives

“…Nucleus independent chemical shielding (NICS) calculations are a common approach to assess ring current effects on chemical shifts [26,52]. DFT GIAO approaches using the B3LYP method with the Pople 6-31G(d) basis set has proven to accurately predict the 13 C shift.…”