TY - JOUR
T1 - Chemical bonding and aromaticity in furan, pyrrole, and thiophene
T2 - A magnetic shielding study
AU - Horner, K.E.
AU - Karadakov, P.B.
PY - 2013/8/16
Y1 - 2013/8/16
N2 - Aromaticity and bonding in furan, pyrrole, and thiophene are investigated through the behavior of the isotropic shielding σ(r) within the regions of space surrounding these molecules. HF-GIAO/6-311++G(d,p) and MP2-GIAO/6-311++G(d,p) (Hartree-Fock and second-order Møller-Plesset perturbation theory utilizing gauge-including atomic orbitals) σ(r) contour plots are constructed using regular two-dimensional 0.05 Å grids in the molecular plane, in horizontal planes 0.5 and 1 Å above it, and in a vertical plane through the heteroatom. The nucleus-independent chemical shifts (NICS) calculated at the ring centers and at 0.5 Å and 1 Å above these centers, NICS(0), NICS(0.5), and NICS(1), respectively, support the widely accepted order of aromaticities thiophene > pyrrole > furan. The results suggest that accurate NICS calculations benefit more from the use of an extended basis set than from the inclusion of dynamical electron correlation effects. The different extents of σ(r) delocalization observed in the horizontal contour plots and other features of σ(r) are also consistent with an aromaticity reduction of the order thiophene > pyrrole > furan. It is suggested that the extent of σ(r) delocalization in σ(r) contour plots in planes 1 Å above the molecular plane could be used for comparing the relative aromaticities of a wide range of aromatic systems.
AB - Aromaticity and bonding in furan, pyrrole, and thiophene are investigated through the behavior of the isotropic shielding σ(r) within the regions of space surrounding these molecules. HF-GIAO/6-311++G(d,p) and MP2-GIAO/6-311++G(d,p) (Hartree-Fock and second-order Møller-Plesset perturbation theory utilizing gauge-including atomic orbitals) σ(r) contour plots are constructed using regular two-dimensional 0.05 Å grids in the molecular plane, in horizontal planes 0.5 and 1 Å above it, and in a vertical plane through the heteroatom. The nucleus-independent chemical shifts (NICS) calculated at the ring centers and at 0.5 Å and 1 Å above these centers, NICS(0), NICS(0.5), and NICS(1), respectively, support the widely accepted order of aromaticities thiophene > pyrrole > furan. The results suggest that accurate NICS calculations benefit more from the use of an extended basis set than from the inclusion of dynamical electron correlation effects. The different extents of σ(r) delocalization observed in the horizontal contour plots and other features of σ(r) are also consistent with an aromaticity reduction of the order thiophene > pyrrole > furan. It is suggested that the extent of σ(r) delocalization in σ(r) contour plots in planes 1 Å above the molecular plane could be used for comparing the relative aromaticities of a wide range of aromatic systems.
UR - http://www.scopus.com/inward/record.url?scp=84882329331&partnerID=8YFLogxK
U2 - 10.1021/jo401319k
DO - 10.1021/jo401319k
M3 - Article
AN - SCOPUS:84882329331
VL - 78
SP - 8037
EP - 8043
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 16
ER -