Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

Ned H. Martin *, Mathew R. Teague and Katherine H. Mills Department of Chemistry and Biochemistry, University of North Carolina Wilmington, 601 South College Road, Wilmington, NC 28403-5932, USA; E-Mails: mattrteague@gmail.com (M.R.T.); khm0327@alum.uncw.edu (K.H.M.) * Author to whom correspondence should be addressed; E-Mail: martinn@uncw.edu. Received: 14 January 2010; in revised form: 17 March 2010 / Accepted: 19 March 2010 / Published: 22 March 2010 Abstract: Through-space isotropic NMR shielding values of a perpendicular diatomic hydrogen probe moved in a 0.5 A grid 2.5 A 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 H