多环化合物的芳香性

介绍了简单判断多环化合物的芳香性、非芳香性、反芳香性、同芳香性及反同芳香性的方法及其在有机化学中的应用.     

Aromaticity Switching in Porphyrinoids

The aromaticity of porphyrinoids can be substantially altered by reversible modification of their original electronic structures. Well‐defined modulators can be used as a means to initiate these modifications, including redox processes, acid–base chemistry, and conformational phenomena. This Focus Review emphasizes the situation for which a single macrocyclic frame alternatively adopts diatropic and paratropic features and both situations are readily and mutually exchangeable. Eventually, such a porphyrinoid transformation can be explored as a suitable element to construct switchable optoelectronic materials.     

An Antiaromatic Electrode‐Active Material Enabling High Capacity and Stable Performance of Rechargeable Batteries

Although aromatic compounds occupy a central position in organic chemistry, antiaromatic compounds have demonstrated little practical utility. Herein we report the application of an antiaromatic compound as an electrode‐active material in rechargeable batteries. The performance of dimesityl‐substituted norcorrole nickel(II) complex (NiNC) as a cathode‐active material was examined with a Li metal anode. A maximum discharge capacity of about 207 mAhg^?1 was maintained after 100 charge/discharge cycles. Moreover, the bipolar redox property of NiNC enables the construction of a Li metal free rechargeable battery. The high performance of NiNC batteries demonstrates a prospective feature of stable antiaromatic compounds as electrode‐active materials.     

Diprotonated [28]Hexaphyrins(1.1.1.1.1.1): Triangular Antiaromatic Macrocycles

Protonation of meso‐aryl [28]hexaphyrins(1.1.1.1.1.1) triggered conformational changes. Whereas protonation with trifluoroacetic acid led to the formation of monoprotonated Möbius aromatic species, protonation with methanesulfonic acid led to the formation of diprotonated triangular antiaromatic species. A peripherally hexaphenylated [28]hexaphyrin was rationally designed and prepared to undergo diprotonation to favorably afford a triangular‐shaped antiaromatic species.     

A Computational Study on a Strategy for Isolating a Stable Cyclopentadienyl Cation

A computational study has been carried out to examine the feasibility of generating a simple monocyclic cyclopentadienyl cation that may be sufficiently stable to isolate and handle at ambient temperatures. Using judicious placement of electron‐withdrawing groups (CF₃) about the ring we have identified a derivative that may approach the stability of isolobal (and isolatable) borole rings, as evaluated by HOMO–LUMO and singlet–triplet gaps. These Cp⁺ derivatives may therefore be an attractive target for synthetic isolation.     

Calculated geometries of dications of bis odd‐membered π‐ring systems containing a NCN fragment and related π‐systems. An opposite out‐of‐plane rotation of the 4n π‐ring subsystems

Quantum chemical calculations have been carried out on dications of bis odd‐membered π‐ring systems containing a NCN fragment and related π‐systems. An opposite out‐of‐plane rotation of both subsystems was found if these systems contain 4n π‐electrons (antiaromatic). A planar situation was found for 4n+2 π‐electrons (aromatic). The geometric representations could be compared with X‐ray crystallographic three‐dimensional structures of related compounds. Calculations at different levels clearly show that separation of the σ‐ and π‐electron contribution is an effective way to elucidate the origin of the geometrical changes. We also give attention to some fundamental aspects of the subsystems related to the 1,3‐azolium cations because of their biochemical relevance such as fast C₂? H proton exchange. We postulate that at least two molecules of water are involved in this process. The significance of a trigonal pyramidal (TP) geometry has been emphasized. © 2001 Wiley Periodicals, Inc. Int J Quantum Chem, 2001     

Synthesis of Di‐peri‐dinaphthoporphyrins by PtCl2‐Mediated Cyclization of Quinodimethane‐type Porphyrins

Di‐peri‐dinaphthoporphyrins can be regarded as a key and common substructure of fused porphyrinoids. PtCl₂‐mediated cycloisomerization reaction of quinodimethane‐type porphyrins provided these doubly fused porphyrins, which exhibit characteristic paratropic ring currents that presumably arise from 24π antiaromatic circuit as a dominant resonance contributor. UV/Vis absorption spectra, cyclic voltammetry, and excited‐state dynamics as well as theoretical calculation support this conclusion.     

Aromaticity Reversal in the Lowest Excited Triplet State of Archetypical Möbius Heteroannulenic Systems

The aromaticity reversal in the lowest triplet state (T₁) of a comparable set of Hückel/Möbius aromatic metalated expanded porphyrins was explored by optical spectroscopy and quantum calculations. In the absorption spectra, the T₁ states of the Möbius aromatic species showed broad, weak, and ill‐defined spectral features with small extinction coefficients, which is in line with typical antiaromatic expanded porphyrins. In combination with quantum calculations, these results indicate that the Möbius aromatic nature of the S₀ state is reversed to Möbius antiaromaticity in the T₁ state. This is the first experimental observation of aromaticity reversal in the T₁ state of Möbius aromatic molecules.     

Revisiting Indolo[3,2-b]carbazole: Synthesis,Structures, Properties,and Applications

Indolo[3,2-b]carbazole presents a π-skeleton with a remarkable electronic structure and interesting potential applications. It is, however, also associated with ambiguity and controversy. Herein, new derivatives of indolo[3,2-b]carbazole are reported and they have enabled a comprehensive study on the electronic structure of indolo[3,2-b]carbazole and the development of a new n-type organic semiconductor. Experimental and computational studies show that indolo[3,2-b]carbazole has a largely localized p-benzoquinonediimine moiety and significant antiaromaticity. When substituted with (4-silylethynyl)phenyl groups, the indolo[3,2-b]carbazole exhibits one-dimensional π–π stacking and functions as an n-type organic semiconductor in solution-processed field effect transistors.     

Theoretical prediction of size‐expansion effect on the C8‐site activity in the modified guanine‐cytosine analogs

Homo/hetero ring‐expanded DNA analogs have been shown to be rationally modified DNA motifs with improved physical or biological properties. In this work, using density functional theory, the stability of these artificial DNA base pairs was examined with regard to three aspects associated with DNA damage, namely deprotonation, H‐abstraction, and H‐radical addition. The effect of size expansion on C8 activity was investigated because C8‐oxidative guanine (G) is one of the most important products of DNA damage. Computational results indicate that the insertion of an aromatic spacer ring in G considerably decreases the electron density over the C8 site, leading to easier deprotonation or H‐abstraction from the C8 site and more difficult H ^. ‐radical attack on the C8 site. However, the opposite phenomenon is observed if the spacer ring is antiaromatic, because of the increased electron density over the C8 site. Moreover, these effects are more prominent the larger the aromaticity or antiaromaticity of the spacer ring. Further analyses, using natural bond orbitals (NBOs) and the nucleus‐independent chemical shift (NICS) index of aromaticity, indicate that the changes of the electron distribution over the C8 site arise because the aromatic spacer ring, involved in the conjugation structure, increases the electron delocalization from the electron‐rich imidazole ring to the diatropic six‐membered rings, while the antiaromatic spacer ring acts as an electron‐donating group, not only inhibiting the above electron delocalization, but also slightly increasing the electron density over the C8 site. The improved stability of these size‐expanded base pairs in different DNA‐damaged environments may encourage their use in practical applications. Copyright © 2009 John Wiley & Sons, Ltd.