对结构化学中价键理论教学的若干思考

通过追踪原始文献,分析结构化学中价键理论部分的教学内容,特别是对氧气分子基态电子结构的处理,发现价键理论不仅能够正确解释或预测分子结构,而且对芳香性、铁磁性等化学键本质的描述表现更优.     

Trapping of the highly strained [5](2,4)quinolinophane system

The highly strained [5](2,4)quinolinophane system can be generated as an intermediate (2b), which is extremely susceptible towards the attack of both nucleophilic and electrophilic species. Addition of water at the carbon bridgehead C2 occurs rapidly and is followed by rearrangements to give a strain free product 10. An unusual carbene addition at the N1C2 bond of 2b is proposed to explain the formation of the strained ‘anti-Bredt’ type olefin 11.     

Aromatic behavior of three membered rings

The aromatic behavior of three membered ring compounds has been analyzed by mean of GAUSSIAN94 theoretical calculations at B3LYP//6-311++G(2d,p) level. Diamagnetic exaltation values obtained from magnetic susceptibilities as well as NICS show the expected aromatic character of the cyclopropyl cation, but the correspondent anion also shows aromatic behavior. This unexpected result is analyzed as well as the character of the other three membered ring derivatives.     

运用密度泛函活性理论的信息论方法研究苯并富烯衍生物的芳香性

文献中已有越来越多的芳香性体系被发现,同时也有越来越多的芳香性指标被提出来,但是如何解释芳香化合物稳定性的起源以及理解芳香性的本质仍然是当今理论化学中一个悬而未决的难题。运用我们新近提出的密度泛函活性理论信息论方法,不久前我们曾对一系列富烯衍生物进行了系统研究并得到了一个全新的认识。本文进一步探讨苯并富烯衍生物的芳香性行为,目的在于考察一个或多个苯环与富烯连接之后其芳香性发生变化的情况。运用香农熵,费舍尔信息,Ghosh-Berkowitz-Parr熵,Onicescu信息能,信息增益,以及相对Rényi熵六个信息量,和四种芳香指标,ASE,HOMA,FLU和NICS,我们系统地研究了信息量和芳香性指标在单、双、三苯并富烯衍生物中的相关性。我们发现,不管是否有苯环与富烯相连,芳香指标和信息量的交叉相关性都是一样的。这表明,虽然苯环本身具有芳香性,但苯环与富烯相连并不能改变富烯的芳香性与反芳香性本质。苯并富烯衍生物与富烯衍生物的芳香性和反芳香性一致。苯并富烯衍生物的芳香性和反芳香性完全取决于富烯本身的芳香性和反芳香性。这些结果为认识和理解复杂体系芳香性和反芳香性起源和本质将提供有益的启示。     

Aromaticity and diatropicity of <Emphasis Type="Italic">p</Emphasis>-polyphenyl-α,ω-quinododimethides

p-Polyphenyl-α,ω-quinododimethides were predicted to be moderately aromatic and diatropic, although they exist only in a single classical resonance structure with no aromatic conjugated circuits. Such a dichotomy was resolved using our graph theory of aromaticity and ring-current diamagnetism. Six-site non-conjugated circuits were found to contribute appreciably to aromaticity and ring-current diamagnetism. Within each quinododimethide molecule, local aromaticity increases on going from the outermost to inner phenylene rings.     

Theoretical Analysis on Magnetic Properties of Conjugated Organic Molecules Containing Borepin

Theoretical study about the magnetic properties of conjugated organic molecules containing borepin with π current density was carried out. 1-(2,4,6-Trimethylphenyl)borepin moiety is the center and other different groups are situated on the both β sides, which are named molecules 1-12 as theoretical model in order to establish the relationship between aromaticity and geometry variation of borepin. The optimized molecular structures of molecules 1-12 are almost keeping planar and the C2-C3 bond length of borepin turns longer from molecule 1 to molecule 12. Different borepin-annulated ring could change the conjugated effect of π-electron between borepin and these borepin-annulated rings. Moreover, the molecule presents antiaromaticity, in other words, the molecule became unstable when the C2-C3 bond length of borepin extended more than ca. 0.1417 nm. But the β position fragment and substituent groups of borepin are not affected in this case, they are still steady. However, the central borepin ring current is counteracted by symmetrical overlap of it with affiliated borepin-annulated ring current. Hence, the central borepin ring breaking would be liable to occur. These molecules have higher vertical ionization potentials(VIPs) and lower vertical electron affinities(VEAs), which suggests that these molecules could easily exist in anionic form.     

酮缺陷对中性和带电六卟啉芳香性影响的直接可视化研究

利用含时密度泛函理论研究了酮缺陷对中性和带电六卟啉芳香性的影响,并使用多维可视化技术给出了该体系基态电荷分布和电子跃迁的直观图像. 研究结果表明,芳香性是决定这类体系基态密立根电荷分布的主要因素;酮缺陷效应使得体系基态的密立根电荷分布更多地局域在六卟啉基团上,在这类体系的五氟苯基取代基上密立根电荷布居较少,同时使得体系的芳香性发生改变. 进一步,通过计算体系的跃迁密度和电荷差分密度,可视化了酮缺陷对中性和带电六卟啉芳香性的影响. 结果表明,酮缺陷加强了体系电荷转移的能力.     

A theoretical study on the aromaticity of thiadiazoles and related compounds

Three different approaches have been considered to determinate the aromatic character of isomeric thiadiazoles. Several indices have been obtained from calculations made in the context of nonlocal (B3LYP) density functional calculations. The results were compared with the existing experimental evidence for analog heterocycles. It is concluded that the thiadiazoles are aromatic compounds, with a larger aromatic character than pyrrole, thiophene and furan. The monoxide and dioxide derivatives are shown to be non-aromatic or antiaromatic molecules.     

1,2,4-Triazolium-5-ylidene and 1,2,4-triazol-3,5-diylidene as new ligands for transition metals

Ab initio calculations show the 1,2,4-triazolium-5-ylidene (3a) and 1,2,4-triazol-3,5-diylidene (4a) are true minima on the potential surface. As expected, 4a is much higher in energy than its triazole isomers 5a, 6a and 8a and the 1,2,4-triazol-3-ylidene (7a). Sodium methoxyde adds to the diquaternary salt of 1,2,4-triazoles (9b,c) to give the corresponding monocationic heterocycles 10b,c in 70 and 50% yield, respectively. One equivalent of silver(I) acetate reacts with 9b leading to the bis(1,2,4-triazolium-5-ylidene)silver(I) complex (11b) in 80% yield. Under the same experimental conditions, but using two equivalents of silver(I) acetate, solid-state one-dimensional polymers 12′b,c featuring the coplanar 1,2,4-triazol-3,5-diylidene ligands coordinated to silver(I) are obtained in 90% yield. 12′c has been fully characterized including a single-crystal X-ray diffraction study.     

Aromaticity of Heterofullerenes C18BxNy (x+y=2) and Their Molecular Ions

The aromaticity of all possible substituted fullerene isomers of C18N2, C18B2, C18BN, and their molecularions which originate from the C20 (Ih) cage were studied by the topological resonance energy (TRE) and the percentage topological resonance energy methods. The relationship between the aromaticity of C18BxNy isomers and the sites where the heteroatoms dope at the C20 (Ih) cage is discussed. Calculation results show that at the neutral and cationic states all the isomers are predicted to be antiaromatic with negative TREs, but their polyvalent anions are predicted to be aromatic with positive TREs. The most stable isomer is formed by heteroatom doping at the 1,11-sites in C18N2, C18B2, and C18BN. Heterofullerenes are more aromatic than C20. The stability order in the neutral states is C18N2>C18BN>C18B2>C20. The stability order in closed-shell is C18B2 8->C20 6->C18BN6->C18N2 4-. This predicts theoretically that their polyvalent anions have high aromaticity.