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Organic electrode materials could revolutionize batteries because of their high energy densities, the use of Earth‐abundant elements, and structural diversity which allows fine‐tuning of electrochemical properties. However, small organic molecules and intermediates formed during their redox cycling in lithium‐ion batteries (LIBs) have high solubility in organic electrolytes, leading to rapid decay of cycling performance. We report the use of three cyclotetrabenzil octaketone macrocycles as cathode materials for LIBs. The rigid and insoluble naphthalene‐based cyclotetrabenzil reversibly accepts eight electrons in a two‐step process with a specific capacity of 279 mAh g⁻¹and a stable cycling performance with ≈65 % capacity retention after 135 cycles. DFT calculations indicate that its reduction increases both ring strain and ring rigidity, as demonstrated by computed high distortion energies, repulsive regions in NCI plots, and close [C⋅⋅⋅C] contacts between the naphthalenes. This work highlights the importance of shape‐persistency and ring strain in the design of redox‐active macrocycles that maintain very low solubility in various redox states.

 

Hydrogen bonding principles are at the core of supramolecular design. This overview features a discussion relating molecular structure to hydrogen bond strengths, highlighting the following electronic effects on hydrogen bonding: electronegativity, steric effects, electrostatic effects, π‐conjugation, and network cooperativity. Historical developments, along with experimental and computational efforts, leading up to the birth of the hydrogen bond concept, the discovery of nonclassical hydrogen bonds (CH…O, OH…π, dihydrogen bonding), and the proposal of hydrogen bond design principles (e.g., secondary electrostatic interactions, resonance‐assisted hydrogen bonding, and aromaticity effects) are outlined. Applications of hydrogen bond design principles are presented.

This article is categorized under:

Structure and Mechanism > Molecular Structures

Structure and Mechanism > Reaction Mechanisms and Catalysis

 

We examine the effects of fusing two benzofurans tos‐indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yieldssyn‐IDBF andsyn‐IIDBF.syn‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character forsyn‐IIDBF. In the case of theanti‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in thesyn‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. Forsyn‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity.

 

Aromaticity is one of the most deeply rooted concepts in chemistry. But why, if two-thirds of existing compounds can be classified as aromatic, is there no consensus on what aromaticity is? σ−, π−, δ−, spherical, Möbius, or all-metal aromaticity… why are so many attributes needed to specify a property? Is aromaticity a dubious concept? This perspective aims to reflect where the aromaticity community is and where it is going. 

Computed nucleus-independent chemical shifts (NICS), contour plots of isotropic magnetic shielding (IMS), and gauge-including magnetically induced current (GIMIC) plots suggest that polarization of the π-system of acridones may perturb the numbers and positions of Clar sextet rings. Decreasing numbers of Clar sextets are connected to experimental observations of a narrowing HOMO–LUMO gap and increased charge mobility in solid-state assemblies of quinacridone and epindolidione.