Symmetry restrictions as starting point for the determination of geometric representations and the dynamics of cyclic ? systems

Abstract

A quasiclassical-state approach was developed for probing π bonding and delocalization energies focused on benzene. A more general picture is now given for neutral n π-conjugated cyclic systems with a geometry distortion from D nh into D 1/2nh (n = 4, 6, 8, . . . , 16), which results in a new aromaticity-antiaromaticity criterion. For n = 6 and 8 the corresponding divalent charged systems were studied in relation to zero-field splittings of the triplet ground state and geometry, respectively. Attention is also given to antiaromatic π-conjugated systems focused on the cyclopropenyl anion, the cyclopentadienyl cation, and the cycloheptatrienyl anion and their relaxed states.

Elementary addition-substitution reactions. H�ckel approach for the description of aromatic and antiaromatic arylmethyl cations

“…HMO calculations using a bond-length-dependent coupling (β) [3,4] confirm this qualitative explanation: [6]CH + 2 < [10]CH + 2 < 1-naphthyl CH + 2 < [14]CH + 2 ≈ 1-pyrenyl CH + 2 < 9-anthracyl CH + 2 < Deviation from this linear relationship is found for the [4n] cyclicmembered methyl cations ([4n]CH + 2 ).…”

“…For the bond-length-dependent resonance integral (β ij ) used in the HMO procedure for πconjugated carbons we derived [3,4]:…”

“…The σ -electron contribution for C-H [8] and C-C [4] linkages are obtained from analytical expressions for R CH and E CH : This means that we are dealing with an asymmetric π-electron distribution that can be described as an (open) pentadienyl cation in a fixed geometry; vide infra. With the HMO approach we arrive to a contribution of less than 10% of the cyclobutadiene part.…”

“…However, in the case of arylmethyl chlorides as benzyl chloride, there will be opposition against interference of the aromaticity of the phenyl ring by the C + exo site (R C1−Cexo = 1.399 Å; 4 1.387 1.372 C 1 -C 11 1.391 1.371 C 4 -C 12 1.420 1.413 C 9 -C 11 1.442 -C 11 -C 12 1.419 1.412 C 10 -C 12 1 3 1.386 1.367 C 3 -C 4 1.406 1.417 C 4 -C 5 1.395 1.392 C 5 -C 6 1.399 1.403 q exo = 0.44 a The geometries of the corresponding proton complexes are presented as diphenylmethyl-, allyl-, pentadienyl-, heptatrienyl-, and nonatetraenyl cation. They show a sigmoidal character for log k versus E π deloc and E π loc .…”

Interconversion between Planar-Triangle, Trigonal-Pyramid and Tetrahedral Configurations of Boron (B(OH)&lt;sub&gt;3&lt;/sub&gt; -B(OH)&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; ), Carbon (CH&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; -CH&lt;sub&gt;3&lt;/sub&gt;X) and for the Group 15 Elements as Nitrogen (NH&lt;sub&gt;3&lt;/sub&gt;-NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup

“…diamantine-triamantane with a C-C distance of 1.704 Å. It seems realistic to assume that both aspects can be explained by (small) changes in the hybridization resulting in (small) angle variation concerning the crucial carbon locations [19].…”