正戊烷异构化反应表征固体超强酸性

详细研究了低温下固体酸催化剂上的正戊烷反应，发现在ＳＯ４＾２－／ＭｘＯｙ型固体超强酸，ＨＭ和ＨＺＳＭ－５沸石表面上正戊烷反应以异构化为主，其反应动力学符合一级可逆反应规律，催化剂的酸强度与正戊烷异构化反应速率常数呈顺变关系，由此提出了一种适合于－１６＜Ｈ０＜－１２的固体酸强度测定方法，解决了该区域内有色样品或高温易分解样品在酸性测量上的难题。     

Photodimerization of 4,6,4′-trimethylangelicin and 6,5-Dimethylangelicin

4,6,4'-Trimethylangelicin and 6,5'-dimethylangelicin form C4-cyclodimers when irradiated in water-ethanol solution. The former compound yields a pyrone-pyrone dimer similar to that formed by psoralens. 6,5'-Dimethylangelicin forms both pyrone-pyrone and pyrone-furan dimers; this unusual dimer has the cis-syn configuration.     

Aggregation and Photodimerization of Areno‐Condensed Annulenes

[18]‐ and [24]Annulenes condensed with three pyrene or phenanthrene ring systems show, in solution, especially in apolar solvents, a strong aggregation evidenced, for example, by concentration‐dependent ¹H‐NMR spectra. However, the fluorescence bands and the fluorescence lifetimes of these compounds depend only to a minor extent on the concentration and correspond essentially to the measurements obtained for the monomer. Among several models discussed, one is favored in which aggregates can be excited, but the emission is due to an almost undisturbed monomer. Even for the pyrene system, an excimer fluorescence cannot be detected. Nevertheless, short‐lived excimers are responsible for the regio‐ and stereoselective photodimerization to belt cyclophanes.     

ESIPT-Inspired Dual-Mode Photoswitches with Fast Molecular Isomerization in the Solid State

Photoswitchable materials have attracted considerable attention in various fields. Developing excellent solid-state dual-mode photoswitches is an important but challenging task. Herein, we propose a new strategy to construct an excited-state intramolecular proton transfer (ESIPT) inspired photoswitch ( DiAH-pht ) that possesses aggregation-induced emission (AIE) features and displays a fast molecular isomerization process characterized by dual-mode behavior in the solid state. Mechanistic studies indicate that introduction of a bulky group can create a folded molecular conformation that provides adequate volume to facilitate photoisomerization and the enhanced ESIPT effect can boost the isomerization process. The feasibility of our strategy was further demonstrated by the activated photoisomerization performance of the Schiff base derivatives. Furthermore, DiAH-pht shows good performance in the fields of dual-mode information encryption and high-density data storage.     

Studies on the Photodimerization of Isoeugenol

Under the irradiation of the ultraviolet light, Isoeugenol (I) undergoes dimerization in acetone to give diisoeugenol (II) and dehydrodiisoeugenol (III). The structures are determined by the comparison of the mixed m. p., I. R. spectra and T. L. C. with synthesized authentic samples. Also the photoreaction mechanism is discussed in detail. The reaction represents a new type and as an exception of photochemical process for the C=C double bond in conjugation with aromatic ring that generally dimerizes to produce cyclobutane type derivatives.     

Halogen‐Bond‐Templated [2+2] Photodimerization in the Solid State: Directed Synthesis and Rare Self‐Inclusion of a Halogenated Product

A ditopic halogen‐bond acceptor organizes a diiodooctafluorostilbene for a [2+2] photodimerization reaction to take place between two stilbene molecules in the solid state. The resultant cyclobutane product is functionalized with halogen atoms and undergoes self‐assembly to form a channel‐type host–guest compound that exhibits a very rare form of self‐inclusion.     

Mechanochemical Cycloreversion of Cyclobutane Observed at the Single Molecule Level

Mechanochemical cycloreversion of cyclobutane is known from ultrasound experiments. It is, however, not clear which forces are required to induce the cycloreversion. In atomic force microscopy (AFM) experiments, on the other hand, it is notoriously difficult to assign the ruptured bond. We have solved this problem through the synthesis of tailored macrocycles, in which the cyclobutane mechanophore is bypassed by an ethylene glycol chain of specific length. This macrocycle is covalently anchored between a glass substrate and an AFM cantilever by polyethylene glycol linkers. Upon mechanical stretching of the macrocycle, cycloreversion occurs, which is identified by a defined length increase of the stretched polymer. The measured length change agrees with the value calculated with the external force explicitly included (EFEI) method. By using two different lengths for the ethylene glycol safety line, the assignment becomes unambiguous. Mechanochemical cycloreversion of cyclobutane is observed at forces above 1.7 nN.     

用常温正丁烷异构化反应表征固体超强酸性

研究了室温下固体超强酸催化剂上正丁烷反应，发现转化率低于50％时，异构化选择性高于95％，正丁烷异构化反应动力学符合一级可逆反应规律，固体超强酸的酸强度与正丁烷异构化反应转化率和速率常数呈顺变关系，与反应表现活化能呈逆变关系．报出了一种新的表征固体超强酸性的实验方法．     

Skeletal Isomerization of <Emphasis Type="Italic">n</Emphasis>-butenes over Solid Acid Catalysts

Conversion reactions of n-butenes over zeolites and amorphous catalysts have been investigated to deduce the factor that determines the selectivity for the skeletal isomerization producing isobutene. The effects of pore structure and acid site concentration on the selectivity for the skeletal isomerization are discussed on various catalysts. The pore structures of FER and CLI zeolites induce the distant locations of butene molecules, accelerating monomolecular skeletal isomerization. On the other hand, acid site concentration determines the preferred reaction path of n-butenes on amorphous catalysts. Oligomerization followed by cracking that produces various hydrocarbons is suppressed on the catalyst with low acid site concentration, resulting in high selectivity for isobutene. The feasibility of monomolecular skeletal isomerization on zeolites and amorphous catalysts is confirmed by its reversibility with high selectivity.     

二杂芳基乙烯光二聚反应与二聚体的晶体结构

通过反-1,2-双(2-苯并唑基)乙烯(BBE)和反-1-(2-苯并咪唑基)-2-(2-苯并唑基)乙烯(BME)的光二聚反应合成了r-1,c-2,t-3,t-4-四(2-苯并唑基)环丁烷(BBC)和r-1,c-2,t-3,t-4-1,3-双(2-苯并咪唑基)-2,4-双(2-苯并唑基)环丁烷(BMC).用元素分析、红外、紫外、核磁共振谱、质谱及X射线衍射表征了二聚体的结构.BBC晶体属三斜晶系,空间群为P1.晶胞参数:a=0.64684(13)nm,b=1.3242(3)nm,c=1.6245(3)nm;α=74.66(3)°,β=78.77(3)°,γ=76.06(3)°,Z=2.BBC晶胞中分子有两种取向,两种取向不同分子的苯并唑平面间存在着π-堆积现象.π-堆积面间的距离在0.330～0.376nm之间,与石墨晶体中分子平面片层间的距离非常接近.BBC和BMC都具有中心对称性,光二聚反应的高度立体选择性以及BBE和BME的光二聚反应不受空气中氧的影响的事实表明它们是经激发单线态历程以面对面的方式进行二聚反应的,本文检测到了BBE和BME在高浓度溶液中的激基缔合物荧光.     

Unclicking the Click: Metal‐Assisted Mechanochemical Cycloreversion of Triazoles Is Possible

The mechanochemical cycloreversion of 1,2,3‐triazole compounds, which serve as unusually stable building blocks in materials and biomolecular chemistry as a result of mild “click chemistry”, remains puzzling. We show that the hitherto discussed straight‐forward retro‐click mechanism of the 1,4‐disubstituted isomer, even if Cu^I catalyzed, can be ruled out in view of more favorable activation free energies of destructive pathways. In stark contrast, the 1,5‐regioiomer can undergo cycloreversion under rather mild mechanochemical conditions owing to its favorable response to the external force in conjunction with standard Ru^II catalysis.     

Photodimerization of 1H-azepine-2,7-dione

1H-Azepine-2,7-dione 2 afforded photodimer 8 by irradiation using a high or low pressure mercury lamp. Photodimer 8 had a unique structure which must have formed with the prototropy in one of the two molecules of compound 2 . Measurement of the fluorescence spectra of 2 indicated a spectrum of the excimer during the dimerization of 2 . Irradiation of the dimer of 2 at its wave-length of maximal absorption failed to cause it to change into a monomer of 2 .     

Unclicking the Click: Metal-Assisted Mechanochemical Cycloreversion of Triazoles Is Possible

The mechanochemical cycloreversion of 1,2,3-triazole compounds, which serve as unusually stable building blocks in materials and biomolecular chemistry as a result of mild “click chemistry”, remains puzzling. We show that the hitherto discussed straight-forward retro-click mechanism of the 1,4-disubstituted isomer, even if Cu^I catalyzed, can be ruled out in view of more favorable activation free energies of destructive pathways. In stark contrast, the 1,5-regioiomer can undergo cycloreversion under rather mild mechanochemical conditions owing to its favorable response to the external force in conjunction with standard Ru^II catalysis.     

High‐Resolution Rotational Spectroscopy Study of the Smallest Sugar Dimer: Interplay of Hydrogen Bonds in the Glycolaldehyde Dimer

Molecular recognition of carbohydrates plays an important role in nature. The aggregation of the smallest sugar, glycolaldehyde, was studied in a conformer‐selective manner using high‐resolution rotational spectroscopy. Two different dimer structures were observed. The most stable conformer reveals C₂‐symmetry by forming two intermolecular hydrogen bonds, giving up the strong intramolecular hydrogen bonds of the monomers and thus showing high hydrogen bond selectivity. By analyzing the spectra of the ¹³C and ¹⁸O isotopologues of the dimer in natural abundance, we could precisely determine the heavy backbone structure of the dimer. Comparison to the monomer structure and the complex with water provides insight into intermolecular interactions. Despite hydrogen bonding being the dominant interaction, precise predictions from quantum‐chemical calculations highly rely on the consideration of dispersion.