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Symmetry 2010, 2(1), 418-436; doi:10.3390/sym2010418

Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

* ,
Department of Chemistry and Biochemistry, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC 28403-5932, USA
* Author to whom correspondence should be addressed.
Received: 14 January 2010 / Revised: 17 March 2010 / Accepted: 19 March 2010 / Published: 22 March 2010
(This article belongs to the Special Issue Aromaticity and Molecular Symmetry)
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Through-space isotropic NMR shielding values of a perpendicular diatomic hydrogen probe moved in a 0.5 Å grid 2.5 Å above several polycyclic aromatic/antiaromatic ring and aromatic/aromatic hydrocarbons were computed with Gaussian 03 at the GIAO HF/6-31G(d,p) level. Combinations of benzene fused with cyclobutadiene, with the tropylium ion, and with the cyclopentadienyl anion were investigated. Subtraction of the isolated H2 isotropic value gave shielding increments(Δσ), which, when plotted against Cartesian coordinates of the probe over each hydrocarbon, gave representations of three-dimensional isotropic shielding increment surfaces. The results are related to the degree of bond length alternation, the extent of electron delocalization, and (for the ions) the NPA charge distribution. The shielding increment data are compared to NICS(1) values computed at the same level; both indicate the degree of aromaticity or antiaromaticity of the component rings.
Keywords: aromaticity; antiaromaticity; NMR shielding; fused hydrocarbons; GIAO; HF/6-31G(d,p); NICS(1) aromaticity; antiaromaticity; NMR shielding; fused hydrocarbons; GIAO; HF/6-31G(d,p); NICS(1)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Martin, N.H.; Teague, M.R.; Mills, K.H. Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons. Symmetry 2010, 2, 418-436.

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