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Is the conventional interpretation of the anisotropic effects of C=C double bonds and aromatic rings in NMR spectra in terms of the p-electron shielding/deshielding contributions correct?

  • Based on the nucleus-independent chemical shift (NICS) concept, isotropic magnetic shielding values have been computed along the three Cartesian axes for ethene, cyclobutadiene, benzene, naphthalene, and benzocyclobutadiene, starting from the molecular/ring center up to 10 angstrom away. These through-space NMR spectroscopic shielding (TSNMRS) values, which reflect the anisotropic effects, have been broken down into contributions from localized- and canonical molecular orbitals (LMOs and CMOs); these contributions revealed that the proton NMR spectroscopic chemical shifts of nuclei that are spatially close to the C?C double bond or the aromatic ring should not be explained in terms of the conventionally accepted p-electron shielding/deshielding effects. In fact, these effects followed the predictions only for the antiaromatic cyclobutadiene ring.

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Author:Marija Baranac-Stojanovic, Andreas Koch, Erich Kleinpeter
ISSN:0947-6539 (print)
Parent Title (English):Chemistry - a European journal
Place of publication:Malden
Document Type:Article
Year of first Publication:2012
Year of Completion:2012
Release Date:2017/03/26
Tag:NMR spectroscopy; ab initio calculations; anisotropic effects; nucleus-independent chemical shift; pi interactions
First Page:370
Last Page:376
Funder:Ministry of Science of the Republic of Serbia; Deutscher Akademischer Austauschdienst (DAAD) [ID: 504 252 70]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer Review:Referiert