Abstract
A recently developed methodology for calculating, analyzing, and visualizing nuclear magnetic shielding densities is used for studying spatial contributions including ring-current contributions to 1H nuclear magnetic resonance (NMR) chemical shifts of aromatic and anti-aromatic free-base porphyrinoids. Our approach allows a visual inspection of the spatial origin of the positive (shielding) and negative (deshielding) contributions to the nuclear magnetic shielding constants. Diatropic and paratropic current-density fluxes yield both shielding and deshielding contributions implying that not merely the tropicity of the current density determines whether the contribution has a shielding or deshielding character. Instead the shielding or deshielding contribution is determined by the direction of the current-density flux with respect to the studied nucleus.
Highlights
This article is dedicated to Professor Riccardo Zanasi on the occasion of his 70th birthday
magnetic shielding densities (MSD) is the spatial contribution to the chemical shifts in nuclear magnetic resonance (NMR) spectroscopy and calculated using the magnetically induced current density (Figure S1)
The largest shielding contribution appears near the studied hydrogen, because of the singular denominator of the vector potential of the magnetic moment of the inner hydrogen
Summary
This article is dedicated to Professor Riccardo Zanasi on the occasion of his 70th birthday He graduated from the University of Modena, Italy in 1975, studying electric and magnetic properties of molecules. He is one of the pioneers in the field of current-density calculations with his first article from 1981 on the ring-current model of the cyclopropenyl cation [1]. Professor Zanasi has published about 70 scientific articles on computational studies of magnetically induced current densities in molecules with “current density” in the title. He is the main developer of the SYSMO code. MSD is the spatial contribution to the chemical shifts in nuclear magnetic resonance (NMR) spectroscopy and calculated using the magnetically induced current density (Figure S1)
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