TY - JOUR
T1 - Analysis of aromatic delocalization
T2 - Individual molecular orbital contributions to nucleus-independent chemical shifts
AU - Heine, Thomas
AU - Ragué Schleyer, Paul V.
AU - Corminboeuf, Clémence
AU - Seifert, Gotthard
AU - Reviakine, Roman
AU - Weber, Jacques
PY - 2003/8/21
Y1 - 2003/8/21
N2 - Individual molecular orbital (MO) contributions to the magnetic shielding of atoms as well as to the nucleus-independent chemical shifts (NICS) of aromatic compounds can be computed by the widely used gauge-including atomic orbital (GIAO) method. Detailed analyses of magnetic shielding MO-NICS contributions provide interpretive insights that complement and extend those given by the localized MO ("dissected NICS", LMO-NICS) method. Applications to (4n + 2) π-electron systems, ranging from [n] annulenes to Dnh S3, S5,and N6H6 2+ rings as well as to D2h cyclobutadiene, show the extent to which their diatropic character results from the σ framework and from the π orbitals. The diatropicity of both these contributions decreases with the number of nodes of the wave function around the ring. The highest-energy orbitals can become paratropic. This is generally the case with the σ orbitals, but is found only for "electron-rich" π systems such as sulfur rings. MO-NICS contributions, which can be interpreted using London-Hückel theory, correlate with inverse ring size.
AB - Individual molecular orbital (MO) contributions to the magnetic shielding of atoms as well as to the nucleus-independent chemical shifts (NICS) of aromatic compounds can be computed by the widely used gauge-including atomic orbital (GIAO) method. Detailed analyses of magnetic shielding MO-NICS contributions provide interpretive insights that complement and extend those given by the localized MO ("dissected NICS", LMO-NICS) method. Applications to (4n + 2) π-electron systems, ranging from [n] annulenes to Dnh S3, S5,and N6H6 2+ rings as well as to D2h cyclobutadiene, show the extent to which their diatropic character results from the σ framework and from the π orbitals. The diatropicity of both these contributions decreases with the number of nodes of the wave function around the ring. The highest-energy orbitals can become paratropic. This is generally the case with the σ orbitals, but is found only for "electron-rich" π systems such as sulfur rings. MO-NICS contributions, which can be interpreted using London-Hückel theory, correlate with inverse ring size.
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U2 - 10.1021/jp035163z
DO - 10.1021/jp035163z
M3 - Article
AN - SCOPUS:0042879754
VL - 107
SP - 6470
EP - 6475
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
SN - 1089-5639
IS - 33
ER -