en
Scientific article
English

Analysis of Aromatic Delocalization: Individual Molecular Orbital Contributions to Nucleus-Independent Chemical Shifts

Published inThe journal of physical chemistry. A, vol. 107, no. 33, p. 6470-6475
Publication date2003
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
Research group
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
Identifiers
ISSN of the journal1089-5639
615views
0downloads

Technical informations

Creation10/06/2009 11:58:52 AM
First validation10/06/2009 11:58:52 AM
Update time03/14/2023 3:16:03 PM
Status update03/14/2023 3:16:03 PM
Last indexation01/15/2024 7:05:36 PM
All rights reserved by Archive ouverte UNIGE and the University of GenevaunigeBlack