Other version: http://pubs.acs.org/cgi-bin/abstract.cgi/jpcafh/2003/107/i33/pdf/jp035163z.pdf
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Analysis of Aromatic Delocalization: Individual Molecular Orbital Contributions to Nucleus-Independent Chemical Shifts |
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Published in | The journal of physical chemistry. A. 2003, vol. 107, no. 33, p. 6470-6475 | |
Abstract | 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 D[nh] S[3], S[5], and N[6]H[6[2+]] rings as well as to D[2h] 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. | |
Keywords | Chemical shifts — Aromaticity — Delocalization — Annulenes — Londo-Hückel | |
Identifiers | DOI: 10.1021/jp035163z | |
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Research group | Groupe Weber | |
Citation (ISO format) | HEINE, Thomas et al. Analysis of Aromatic Delocalization: Individual Molecular Orbital Contributions to Nucleus-Independent Chemical Shifts. In: The journal of physical chemistry. A, 2003, vol. 107, n° 33, p. 6470-6475. doi: 10.1021/jp035163z https://archive-ouverte.unige.ch/unige:3702 |