A retrospective appraisal of the Pople point‐dipole model of ‘‘ring‐current’’ effects on1H‐NMR chemical shifts in planar, condensed, benzenoid hydrocarbons

1981 ◽  
Vol 75 (2) ◽  
pp. 793-797 ◽  
Author(s):  
R. B. Mallion
Keyword(s):  
Ring Current ◽  
Chemical Shifts ◽  
Dipole Model ◽  
Point Dipole ◽  
Benzenoid Hydrocarbons ◽  
Nmr Chemical Shifts

scholarly journals Spatial Contributions to 1H NMR Chemical Shifts of Free-Base Porphyrinoids

Chemistry ◽  
2021 ◽  
Vol 3 (3) ◽  
pp. 1005-1021
Author(s):  
Heike Fliegl ◽  
Maria Dimitrova ◽  
Raphael J. F. Berger ◽  
Dage Sundholm
Keyword(s):  
Current Density ◽  
Visual Inspection ◽  
Ring Current ◽  
Chemical Shifts ◽  
Magnetic Shielding ◽  
Free Base ◽  
Nmr Chemical Shifts ◽  
1H Nuclear Magnetic Resonance ◽  
Shielding Constants ◽  
Nuclear Magnetic

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.

scholarly journals Is (benzene)Cr(CO)3 really more aromatic than benzene?

2017 ◽  
Vol 95 (3) ◽  
pp. 263-270 ◽  
Author(s):  
Amnon Stanger
Keyword(s):  
Local Ring ◽  
Excellent Agreement ◽  
Ring Current ◽  
Chemical Shifts ◽  
Experimental Results ◽  
Nmr Chemical Shifts ◽  
Ring Currents ◽  
Global And Local

(benzene)Cr(CO)3 was claimed to be more aromatic than benzene, based on the central 1H Me chemical shifts in dimethyldihydropyrene annulated to it. In this paper, several dihydropyrenes are computationally investigated. NICS-scan methods are used to assess the ring current properties, and NMR calculations are used for obtaining NMR chemical shifts. The parent and four benz-annulated dihydropyrenes show excellent agreement with the experimental results, reported by R. Mitchell in several papers. The effect of annulating the antiaromatic cyclobutadiene was shown to be larger than that of benzene and to change the type of ring currents; while benz-annulated dihydropyrenes maintain local 14-annulene and local benzenic ring currents, the cyclobutadiene-annulated dihydropyrenes show global (and local) ring currents. A NICS-scan study of (benzene)Cr(CO)3 and a NICS-XY-scan study of the (CO)3Cr(C6H4)-annulated to dihydropyrene show that the benzene in the Cr complex is at most aromatic as benzene, probably somewhat less. A detailed study of the 1H chemical shifts suggests that the experimental results were somewhat misinterpreted, and that (benzene)Cr(CO)3 is at most as aromatic as benzene.

Relativistic and Dynamic effects are needed to correctly model the 1H NMR Chemical Shifts of an Iridium Polyhydride Cluster

2020 ◽  
Author(s):  
Abril C. Castro ◽  
David Balcells ◽  
Michal Repisky ◽  
Trygve Helgaker ◽  
Michele Cascella
Keyword(s):  
1H Nmr ◽  
Chemical Shifts ◽  
Dynamic Effects ◽  
Nmr Chemical Shifts
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