Abstract
The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzenoid and quinoid tautomeric structures such as benzodifurantrione and phenazine-type molecules have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Rague Schleyer and visualized as iso-chemical- shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the partial aromaticity of the studied compounds. In the case of the surprisingly more stable quinoid tautomers, the aromaticity-synonymous with stability due to the conjugation of π electrons and lone pairs-was not found to be particularly reduced.
Highlights
The shielding at or above the center of aromatic ring systems and realized by the concept of nucleus independent chemical shielding (NICS),[1] is a parameter that can be used to characterize the aromaticity of organic compounds
In another study,[23] we extended our examination to keto–enol tautomers and push-pull structures in order to identify the size of the partial aromaticity
The influence on the stability of structures arising from the delocalization of π and lone pair electrons has not been properly addressed and because the spatial magnetic properties of conjugated moieties has proven to be very sensitive to these influences,[3,18] through-space NMR shieldings (TSNMRS) were computed and appropriately examined as the central topic of this paper
Summary
The shielding at or above the center of aromatic ring systems and realized by the concept of nucleus independent chemical shielding (NICS),[1] is a parameter that can be used to characterize the aromaticity of organic compounds. The influence on the stability of structures arising from the delocalization of π and lone pair electrons (in the case of six electrons, partial aromaticity) has not been properly addressed and because the spatial magnetic properties of conjugated moieties has proven to be very sensitive to these influences,[3,18] TSNMRS were computed and appropriately examined as the central topic of this paper.
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