π-Conjugated Anions: From Carbon-Rich Anions to Charged Carbon Allotropes

Abstract

Stable π-conjugated anions are formed in the reaction of π-conjugated systems with alkali metals. Reactivity, aromatic properties and aggregation of the anions are described.

An Analysis of Topological Ring-Currents and their Use in Assessing the Annulene-Within-an-Annulene Model for Super-Ring Conjugated Systems

“…22, and in the fifth column of Table 6, here, the topological bond-currents in the central ring of 7 are described as 'mixed'; structure 7, therefore, likewise does not obey the strict provisions of the AWA rule. [14][15][16][17][18][19][20][21][22][23][24] By contrast, we present new results (in Figure 8 and Table 6) for another structure ([9]-coronaphene (6)) which, like anti-kekulene (7), has a [4m] carbon-atom periphery and also a [4n]-membered central-ring. This is seen ( Figure 8 and Table 6) to exhibit diamagnetic ringcurrents in the peripheral rings and a paramagnetic ringcurrent in the central ring.…”

“…Acta 86 (2013) 387. (1), azulenoid-kekulene (3), and anti-kekulene (7) were initially given in Table 1 (benzene)) calculated from equation (17), with topological ring-currents, (J i / J benzene ), deduced from equation (14) and relative ring-areas, (s i / s benzene ), evaluated via equation (16) (for 3 and 7) or (in the case of structures 1, 2, 4, 5 and 6) according to the procedures described in the paragraph following equation (16), in the text. (c) A positive value (found for structures 1-6) indicates overall diamagnetic 'London' susceptibility: a negative value (as in the sole case of anti-kekulene (7)) indicates an overall paramagnetic 'London' susceptibility (all in a direction at right angles to their assumed molecular-planes).…”

“…As mentioned, these (idealised) ring-areas were estimated from equation (16) in the case of structures 3 and 7 and, in the case of the central rings of 1, 2, 4, 5, and 6, by counting the number of hexagons that would fill the 'hole' in the otherwise completely tessellated hexagonal-network. The resulting 'London' susceptibility-ratios for 1-7 are presented in the right-hand column of Table 6.…”

“…[9][10][11] Application of this approach will be illustrated by using it to compute numerical values of ring currents and bond currents in order to re-enforce a recent re-evaluation 12,13 of the 'AnnuleneWithin-an-Annulene' (AWA) model, [14][15][16][17][18][19][20][21][22][23][24] a model which has been of interest to several groups of workers, [14][15][16][17][18][19][20][21][22][23][24] especially over the last decade or so. [16][17][18][19][20][21][22][23][24] The simplicity of this HLPM topological formalism is that, unlike with most other methods for calculating ring currents, there is no requirement to determine atomic coordinates in order to perform these calculations. All that is required is the connectivity matrix and the geometric areas of the constituent rings, and we choose to perform the calculation in two stages -a purely topological stage, followed by one that involves the actual geometry of the conjugated system.…”

“…The AWA model arises in the context of conjugated systems that consist of a central ring of carbon atoms joined by 'transverse' 25 ('spokes') 21 bonds to a larger, outer ring, as in 26,27 It has long been known [28][29][30][31] that annulenes -and we refer here strictly to the classic, monocyclic annulenes -are associated with paramagnetic π-electron 26,27 is said to obey the AWA model [14][15][16][17][18][19][20][21][22][23][24] if both its central ring and its outer perimeter bear calculated π-electron currents according to the pattern described above -implying that the inner and outer rings effectively behave as if they were independent annulenes. Most super-ring 26,27 structures seem, however, to violate the AWA model when tested against the results of ab-initio ipso-centric calculations [17][18][19][20][21]32,33 and of 'pseudo-π' calculations 34 of the type frequently presented by Fowler and co-workers, and also when confronted with topological [9][10][11] π-electron ring-currents and bond-currents that we ourselves have calculated 22,23 by means of the HLPM approach.…”