Benzenium Ion: Aromatic as the π-Complex or Antiaromatic as the σ-Complex Being Somewhat Similar to the Cyclopentadienyl Cation

Abstract

The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of the benzenium cation (C 6 H 7 + ) 1 and of ±I/M-substituted analogues C 6 H 6 X + 3−8 [X = −Me, −CF 3 , −NH 2 , −NO 2 , −NO, −SiH 3 ] have been calculated using the gauge-independent atomic orbital perturbation method employing the nucleus-independent chemical shift concept, and iso-chemical-shielding surfaces of various sizes and directions have been observed. The TSNMRS values were employed to compare the spatial magnetic properties (TSNMRS) of benzene and the benzenium ion 1 and then further compared with analogues 3−8, to answer the question whether the electronic structures of 1 and 3−8 are still similar to those of aromatic species or somewhat similar to the antiaromatic cyclopentadienyl cation 2, supported by structural data and δ( 13 C)/ppm values.

Solvation in nitration of benzene and the valence electronic structure of the Wheland intermediate

“…Another concern is the valence electronic structure of the s-complex, which has been of interest to researchers. [25][26][27][28][29][30] In electrophilic aromatic substitution reactions, aromatic stabilisation in the original sixmembered ring is destroyed, and a s-bonding is formed instead. The electronic origin of alternative stabilisation in the s-complex is of great interest, and analyses based on resonance theory with quantitative calculations are desirable.…”

Bent Allenes or Di-1,3-betaines—An Answer Given on the Magnetic Criterion

“…If the NMR characterization of the electronic structure is omitted, and only energy and/or geometry assignments are employed, misclassifications can happen. For example, when employing our through-space NMR shielding concept (TSNMRS) − to qualify and quantify the spatial magnetic properties (actually, the widely used concept of anisotropy/ring current effect in 1 H NMR spectroscopy) of the studied conjugated species, the existence of (anti)­aromaticity, − quasi-, captodative, homo-, Y-, and chelato-aromaticity, and the electronic structure of benzyne and of the benzenium cation, which were assigned on the energy and/or geometry criterion, could be confirmed or ruled out. Along this paper, the experimentally available and the computed energy structural and magnetic data of a number of conjugated compounds will be employed to discuss a structural question, which has been contrarily discussed recently.…”