大环轮烯的合成及其NMR谱特征

论述了大环轮烯、去氢轮烯、架桥轮烯及氮杂轮烯、氧杂轮烯、硫杂轮烯的合成方法;轮烯、去氧轮烯[4n+2]、[4n]体系以及杂原子轮烯[4n+1]、[4n-1]体系的NMR谱的特征;还介绍了近两年大环轮烯研究成果及发展趋势。     

芳香性研究的最新进展: Möbius芳烃和富勒烯基芳香性全反式[18]轮烯

芳香性反式轮烯结构富勒烯具有高共轭性, 是潜在的优良的光能捕获分子. 综述了Möbius芳烃和芳香性反式轮烯结构富勒烯的合成和性质研究的最新进展, 并展望了其今后的发展方向.     

芳香性研究的最新进展:Mbius芳烃和富勒烯基芳香性全反式[18]轮烯

芳香性反式轮烯结构富勒烯具有高共轭性,是潜在的优良的光能捕获分子.综述了M?bius芳烃和芳香性反式轮烯结构富勒烯的合成和性质研究的最新进展,并展望了其今后的发展方向.     

芳香性研究的最新进展:M(o)bius芳烃和富勒烯基芳香性全反式[18]轮烯

芳香性反式轮烯结构富勒烯具有高共轭性,是潜在的优良的光能捕获分子.综述了M(o)bius芳烃和芳香性反式轮烯结构富勒烯的合成和性质研究的最新进展,并展望了其今后的发展方向.     

简便合成3,3'-联-1,6-亚甲基桥[10]轮烯

以1,6-二甲酰基环庚三烯为原料通过10π电子环化反应等3步反应制备了3-溴代-1,6-亚甲基桥[10]轮烯, 通过3-溴代-1,6-亚甲基桥[10]轮烯的碱诱导的偶联反应, 简便地合成3,3'-联-1,6-亚甲基桥[10]轮烯, 并用NMR, MS等波谱进行了表征.     

简便合成3,3′-联-1，6-亚甲基桥[10]轮烯

以1，6-二甲酰基环庚三烯为原料通过10π电子环化反应等3步反应制备了3-溴代-1，6-亚甲基桥[10]轮烯，通过3-溴代-1,6-亚甲基桥[10]轮烯的碱诱导的偶联反应，简便地合成3，3′-联-1，6-亚甲基桥[10]轮烯，并用NMR，MS等波谱进行了表征。     

四氮［14］轮烯合镍（Ⅱ）配合物的研究（Ⅰ）──取代四氮［14］轮烯合镍（Ⅱ）配合物的合成及其表征

四氮［１４］轮烯类配合物在性质上与卟啉、酞菁类化合物具有许多相似性．本文利用模板反应，合成了２个四氮［１４］轮烯合镍（Ⅱ）配合物及６个四氮［１４］轮烯合镍（Ⅲ）配合物的衍生物，其中６个未见文献报道。对所有化合物进行了ＥＡ、ＩＲ、ＵＶ、１ＨＮＭＲ、ＭＳ等波谱表征．     

新型N-氨基取代的1,6-亚甲基桥[10]轮烯-3,4-二甲酰亚胺的无溶剂合成

以1,6-亚甲基桥[10]轮烯-3,4-二乙酯为原料,简便地合成了二甲酸酐(2);2与肼在氮气保护下,无溶剂于170 ℃反应30 min,以较高收率合成了4个新型N-氨基取代的1,6-亚甲基桥[10]轮烯-3,4-二甲酰亚胺,其结构经1H NMR, 13C NMR, MS及HR-MS表征.     

新型N-取代-R-氧基羰基-1,6-亚甲基桥[10]轮烯-3,4-二甲酰亚胺的无溶剂合成

在无溶剂条件下,1,6-亚甲基桥[10]轮烯-3,4-二甲酸酐与尿素反应制得1,6-亚甲基桥[10]轮烯-3,4-二甲酰亚胺(2);2与KOH的甲醇溶液于常温反应得1,6-亚甲基桥[10]轮烯-3,4-二甲酰亚胺钾(3);3与氯甲酸酯反应合成了4个新型的N-酯基取代的1,6-亚甲基桥[10]轮烯-3,4-二甲酰亚胺,其结构经1H NMR,13C NMR,IR,MS和HR-MS表征。     

四氮（14）轮烯合镍（Ⅱ）配合物的研究（I）——取代四氮（4）轮烯…

四氮（１４）轮烯类配合物在性质上与卟啉，酞菁类化合物具有有许多相似性，本文利用模板反应，合成了２个四氮（１４）轮烯合镍（ＩＩ）配合物及６个四氮（１４）轮烯合镍（Ⅲ）配合物的衍生物，其中６个未见文献报道，对所有化合物进行了ＥＡ、ＩＲ、ＵＶ、ＨＮＭＲ、ＭＳ等波谱表征。     

A dissected ring current model for assessing magnetic aromaticity: a general approach for both organic and inorganic rings

A model based on classical electrodynamics is used to measure the strength of ring currents of different molecular orbitals, i.e., σ- and π-orbitals, and characteristics of ring current loops, i.e., ring current radii and height of current loops above/below the ring planes, among a number of organic as well as inorganic molecules. For the π-current, the present model represents an improvement of previous approaches to determine ring current intensity. It is proven that the present model is more precise than previous models as they could not explain presence of the minimum in the plot of NICS(πzz) versus distance close to the ring plane. Variations in the charge of molecules and the types of constituent atoms of each species affect the ring current radii of both σ- and π-current loops as well as the height of π-current loops above/below the ring plane. It is suggested that variation in the distribution of the one-electron density in different systems is the main source of differences of the ring current characteristics.     

Aromaticity of N-heterocyclic carbene and its analogues: Magnetically induced ring current perspective

The N-heterocyclic carbene, imidazole-2-ylidene, and its main group (13-15) analogues contain cyclically conjugated 6π electrons. Experimental ¹H nuclear magnetic resonance (NMR) spectra suggest an increase in aromaticity along a period from left to right. Whereas the order along a group is as follows: period 2 > period 5 > period 4 > period 3 due to change in structure. To understand the order of aromaticity, the magnetically induced ring currents of the molecules are calculated using aromatic ring current shielding, gauge-including magnetically induced currents (GIMIC) method and Stanger's σ-model applying the gauge-including atomic orbitals NMR technique. It is found that GIMIC best describes the order of aromaticity especially along a group where current-profile changes on the bivalent atom down a group due to change in electron density. Moreover, the GIMIC provides the visualization of current by sign modulus and the anisotropy of the induced current density plots.     

Benzonorcorrole NiII Complexes: Enhancement of Paratropic Ring Current and Singlet Diradical Character by Benzo‐Fusion

Fused benzene rings to antiaromatic compounds generally improve their stability but attenuate their antiaromaticity. The opposite case is now reported. Ni^II benzonorcorroles were synthesized and the effect of benzo‐fusion on the antiaromaticity was elucidated. The benzo‐fusion resulted in significant decrease of the HOMO–LUMO gaps and enhancement of the paratropic ring current effect. Furthermore, the introduction of the benzo groups induced singlet diradical character in the antiaromatic porphyrinoid.     

Theoretical strategies toward stabilization of singlet remote N‐heterocyclic carbenes

Theoretical investigations predict that the singlet states of ylide‐substituted remote carbenes are significantly stable and comparable to those of experimentally known NHCs. They are also found to be strongly σ‐donating in nature as evident from an evaluation of the carbonyl stretching frequencies (ν_CO) of their complexes with the [Rh(CO)₂Cl] fragment. NICS and QTAIM based bond magnetizability calculations indicate the presence of cyclic electron delocalization in majority of the molecules. © 2016 Wiley Periodicals, Inc.     

Understanding the ring current effects on magnetic shielding of hydrogen and carbon nuclei in naphthalene and anthracene

The local response to an external magnetic field normal to the molecular plane of naphthalene and anthracene was investigated via current density and magnetic shielding density maps. The Biot-Savart law shows that the deshielding caused by pi-ring currents in naphthalene is stronger for alpha- than for beta-protons due to geometrical factors. The shielding tensor of the carbon nuclei in both molecules is strongly anisotropic and its out-of-plane component determines the up-field chemical shift of (13)C in nuclear magnetic resonance spectra. The pi-ring currents flowing beyond the C-skeleton in front of a probe carbon nucleus, and on remote parts of the molecular perimeter, yield positive contributions to the out-of-plane component of carbon shielding as big as approximately 10-15% of the total values. Near Hartree-Fock estimates of magnetizability and magnetic shielding at the nuclei fully consistent with the current model are reported.     

Ion solvation in 3-methyl-2-oxazolidone

In continuing previous studies of the solvation behavior of electrolytes in nonaqueous media, a series of tetraalkylammonium tetraphenylborates, cesium and rubidium tetraphenylborates, tetraalkylammonium perchlorates, and tetraphenylarsonium chloride were investigated by proton magnetic resonance spectroscopy in 3-methyl-2-oxazolidone, a solvent with high dielectric constant, high polarity, and wide liquid range. In this study, as in a previous investigation, it was found that salt solutions containing the tetraphenylborate anion were found to shift the proton peaks upfield, indicating an increase in electron density around solvent protons. In this study the same effect has been noted for tetraphenylborate as well as tetraphenylarsonium ion and is attributed to the large diamagnetic anisotropy of the aromatic solute molecules which results in circulation of electrons induced by the magnetic field. This ring current causes shielding of the solvent protons, and the shielding increases as the concentration of aromatic solute increases, resulting in upfield morement of chemical shift irrespective of whether the aromatic moiety is the cation or anion.     

From C58 to C62 and back: Stability,structural similarity,and ring current

An increasing number of observations show that non‐classical isomers may play an important role in the formation of fullerenes and their exo‐ and endo‐derivatives. A quantum‐mechanical study of all classical isomers of C₅₈, C₆₀, and C₆₂, and all non‐classical isomers with at most one square or heptagonal face, was carried out. Calculations at the B3LYP/6‐31G* level show that the favored isomers of C₅₈, C₆₀, and C₆₂ have closely related structures and suggest plausible inter‐conversion and growth pathways among low‐energy isomers. Similarity of the favored structures is reinforced by comparison of calculated ring currents induced on faces of these polyhedral cages by radial external magnetic fields, implying patterns of magnetic response similar to those of the stable, isolated‐pentagon C₆₀ molecule. © 2016 Wiley Periodicals, Inc.     

A unified orbital model of delocalised and localised currents in monocycles, from annulenes to azabora-heterocycles

Why are some (4n+2)π systems aromatic, and some not? The ipsocentric approach to the calculation of the current density induced in a molecule by an external magnetic field predicts a four‐electron diatropic (aromatic) ring current for (4n+2)π carbocycles and a two‐electron paratropic (antiaromatic) current for (4n)π carbocycles. With the inclusion of an electronegativity parameter, an ipsocentric frontier‐orbital model also predicts the transition from delocalised currents in carbocycles to nitrogen‐localised currents in alternating azabora‐heterocycles, which rationalises the differences in (magnetic) aromaticity between these isoelectronic π‐conjugated systems. Ab initio valence‐bond calculations confirm the localisation predicted by the naïve model, and coupled‐Hartree–Fock calculations give current‐density maps that exhibit the predicted delocalised‐to‐localised/carbocycle–heterocycle transition.