Dianion and Tetraanion of [2₄] Paracyclophanetetraene—New Unusual Perimeter Systems

Abstract

plified additivity of the volumes of the pure substances was assumed (from the densities of CO,[iO1). According to Figure 2 the solubility increases monotonously with increasing pressure and reaches a value of ca. 40 g-dm-3 at 250 bar. The slopes of the curves differ only slightly above and below the critical temperature of C02. However, at temperatures below the critical point of COz, some of the curves intersect at a concentration of ca. 35 g.dm-3 and a pressure of ca. 180 bar.The systems squalane + C0215' and caffeine + CO2I9] be-

Switching between Local and Global Aromaticity in a Conjugated Macrocycle for High‐Performance Organic Sodium‐Ion Battery Anodes

“…The ACID plot of PCT 2− shows a strong diatropic ring current along the [24]annulene substructure (Figure b right), indicating that the two additional electrons delocalize over the macrocyclic substructure and create a globally aromatic [4 n +2] π‐electron system that obeys Hückel's rule. The diatropic ring current mainly flows along the perimeter of the macrocycle, confirming conclusions previously drawn from 1 H NMR measurements of the dianion, which experimentally indicated its globally aromatic nature . No local ring currents were observed in the ACID plots of PCT 2− .…”

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

“…Cyclophane 2, which was first synthesized and reduced using lithium, [6a] yielded stable di-and tetraanions. [10] The dianion of 2 with the better reducing metal (potassium) appears immediately after a brief contact with the metal, but, in contrast to 1, both lithium and potassium salts exhibit very similar 1 Hand 13 C-NMR spectra. [9] Further reduction of 1 2-with potassium produces a new 1 H-NMR spectrum, attributable to the tetraanion.…”

“…While the reduction of 2 with lithium led to stable di-and tetraanions, [10] the reduction with potassium yielded a stable dianion, and only after a long contact with the metal did further reduction to the unstable tetraanion occur. The opposite behavior was found in cyclophane 1.…”

Global Aromaticity and Antiaromaticity in Porphyrin Nanoring Anions

“…We show that the tetraanion is antiaromatic (88 p-electrons), and the hexaanion is aromatic (90 p-electrons). Thec hemical reduction of annulenes was widely explored during the 1980s, [23] but there are few recent examples of macrocycles that become aromatic in anionic reduced states, [19] and it was not clear whether this strategy could be used in complex heterocyclic macrocycles,such as porphyrin nanorings.…”