Both
traditional and novel techniques were employed in
this work
for magnetic shielding evaluation to shed new light on the magnetic
and aromaticity properties of benzene and 12 [n]paracyclophanes
with n = 3–14. Density functional theory (DFT)
with the B3LYP functional and all-electron Jorge-ATZP and x2c-TZVPPall-s
basis sets was utilized for geometry optimization and magnetic shielding
calculations, respectively. Additionally, the 6-311+G(d,p) basis set
was incorporated for the purpose of comparing the magnetic shielding
results. In addition to traditional evaluations such as NICS/NICS
zz
-Scan, and 2D-3D σiso(r)/σ
zz
(r) maps, two new techniques were implemented: bendable grids (BGs)
and cylindrical grids (CGs) of ghost atoms (Bqs). BGs allow for the
recording of magnetic shielding from the bent ring levels of [n]pCPs, while CGs provide tubular magnetic shielding scan
(TMSS) maps detailing the magnetic shielding from a cylindrical region
above and below the ring frame. Our findings suggest that smaller
[n]pCPs with n < 6 exhibit deviations
in the magnetic shielding above and below the ring, indicating a broken
electron delocalization under the ring. In contrast, larger [n]pCPs tend to behave similarly to benzene in terms of magnetic
shielding. Moreover, we found that shorter polymethylene chains of
[n]pCPs exhibit significantly higher magnetic shielding
interactions with the ring. Both of the above techniques offer new
and promising tools for characterizing nonplanar aromatic compounds,
thereby contributing to a deeper understanding of their magnetic and
electronic properties.