Azulene in Polymers and Their Properties

Azulene, a unique isomer of naphthalene, has received much interest from researchers in different fields due to its unusual chemical structure with a negatively charged 5‐membered ring fused with a positively charged 7‐membered ring. In particular, incorporation of azulene into polymers has led to many interesting properties. This minireview covers functionalization methods of azulene at its various positions of 5‐ and 7‐membered rings to form azulene derivatives including azulene monomers, and gives an overview of a wide range of azulene‐containing polymers including poly(1,3‐azulene), azulene‐based copolymers with connectivity at 1,3‐positions of the 5‐membered ring, or 4,7‐positions of the 7‐membered ring, as well as copolymers with azulene units as side chains. Their chemical and physical properties together with applications of azulene‐containing polymers have also been summarized.     

杯吡咯功能化合物的研究与应用

综述了近几年杯吡咯新型大环化合物在功能化修饰和分子识别等方面的研究进展.在近3年里,人们合成了许多新的meso- 、C-rim修饰的,腔体被延伸化的和环体扩张的杯吡咯大环化合物.主要讨论了功能化衍生物的合成、色谱固定相、分子识别作用及其在阴离子传感器上的应用.     

Thienyl—Appended porphyrins: Synthesis,photophysical and electrochemical properties,and their applications

This review focuses on the synthesis, photophysical and electrochemical properties of thienyl porphyrins where processes such as electron transfer, energy transfer and electropolymerisation are discussed. The purpose of this review is to examine the influence of the thienyl ring, whether it be directly connected (via meso and β positions) or indirectly connected (via a covalent linker or axial coordination) on the ground and excited state electronic properties of the porphyrin macrocycle. Additionally, the importance of the electronic properties of a bridging oligothiophene between the porphyrin and another centre in supramolecular systems is discussed. Also included are applications of thienyl porphyrins in such areas as catalysis, therapeutics, (opto)electronics and electron-transfer/light-harvesting systems.     

Recent synthetic strategies of medicinally important imidazothiadiazoles

Imidazothiadiazole is a fundamental fused heterocyclic compound containing imidazole and thiadiazole ring systems. This versatile framework has significant applications in pharmaceutical chemistry and also possessed a remarkable biological profile. The derivatives of imidazo[2,1-b][1,3,4]thiadiazole have a broad spectrum of biological applications such as antitumor, tubulin inhibitor, anticancer, antifungal, anti-inflammatory, antimicrobial, antitubercular, anticonvulsant, antibacterial and as enzyme inhibitors. These derivatives also play a significant role in the development of non-linear optics and photo-electronics. Synthesis of this fused bicyclic compound mainly involved the reaction between 2-amino-1,3,4-thiadiazoles and α-haloketones, with different substitutions at the 2, 5, and 6 positions of the ring system. Moreover, microwave assisted multicomponent and C–C coupling reactions in the presence of catalysts or under solvent free reaction conditions were found to be reliable and valuable approaches. This review is a concerted approach to describe the synthesis and applications of imidazo[2,1-b][1,3,4] thiadiazole derivatives reported during 2015–2022.     

Hydrogen-deuterium exchange in dimethylpyridines

Dimethylpyridines undergo deuterium-hydrogen exchange when heated in deuterium oxide containing potassium carbonate at ring positions 2 and 6 when these positions are unsubstituted and at methyl groups located at ring positions 2,4, and 6 exclusively.     

NMR spectra of pyrimidines

The chemical shifts of the protons in the even positions of the pyrimidine ring in 2- and 4-substituted pyrimidines in dimethyl sulfoxide solutions were determined. The correlation equations that link the relative chemical shifts (with allowance for corrections for the magnetic anisotropy of the substituents and the ring) with the F and R substituent constants were calculated. The ratios obtained were analyzed by comparison with the corresponding correlation equations for monosubstituted benzenes. The reasons for the significant increase in the transmission of the conjugation effects of the substituents to the even positions of the pyrimidine ring as compared with the meta positions of the benzene ring and the appreciable weakening of the conductivity of their inductive effects when the heteroring nitrogen atom is situated between a resonating proton and the substituent are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 673–677, May, 1978.     

具有表皮生长因子受体抑制活性的喹唑啉衍生物研究进展

综述了近十年来具有表皮生长因子受体(EGFR)抑制活性的喹唑啉衍生物的国内外研究进展,按照喹唑啉环上不同位置上的取代基类型分为四类,介绍了化合物不同位置上取代基对此类化合物生物活性的影响,并对其发展趋势和应用前景作了展望.     

Molecular complexes of paraquat with anilines

The U V-VIS spectra of molecular complexes of paraquat with ring and N-substituted anilines have been recorded in methanol and 50% v/v aqueous methanol. All the complexes exhibited well-resolved charge transfer bands in the wavelength region where neither of the components have any absorption. The energies of charge transfer bands of the substituted aniline-paraquat complexes bear linear relationships with the ionization potentials obtained from the substituted aniline-TCNE complexes, indicating π - π interaction between paraquat and the donors. Both ring and N-substituents have effects on the positions of the CT bands as well as on the stabilities of the complexes. The positions of the CT bands are shifted to shorter wavelengths and the stabilities of the complexes decrease on going from methanol to aqueous. methanol.     

Ferroelectric Liquid Crystals. Part 9. Laterally substituted phenyl benzoates incorporating a trans-1,4-disubstituted cyclohexane ring

About 65 diverse phenyl benzoates incorporating a trans-1,4-disubstituted cyclohexane ring and at least one lateral substituent have been synthesised. The dependence of the liquid-crystal transition temperatures of these materials on various lateral substituents (F, Cl, CN, and Br) in different positions of the esters has been investigated systematically. The influence of up to four F-atoms in various positions of a standard ester has been thoroughly studied and the optimum combination for a broad smectic C mesomorphic range established. In consequence, three homologous series incorporating the 4-alkoxy-2,3-difluorobenzoic-acid moiety were prepared. An additional C?C bond was introduced into the alkyl chain attached to the cyclohexane ring of some of these esters and the resulting modifications of the transition temperatures determined. Three ester series incorporating a lateral substituent and the optically active (+)-(S)-(1-methylheptyl)oxy substituent have also been synthesised, and similar effects have been observed. These materials can be used as important components of commercial chiral smectic C mixtures for electro-optic display device applications.     

Shape-persistent macrocycles: from molecules to materials

Shape-persistent macrocycles with an interior in the nanometer regime allow the attachment of (functional) side groups at defined positions at the ring. These side groups can have either a fixed orientation relative to the molecular backbone or they can adapt their orientation according to an external stimulus. The properties and applications of the compounds depend strongly on the orientation of these side groups. Macrocycles with intraannular or adaptable long alkyl groups display a new design principle for discotic liquid crystals. Macrocycles with extraannular (oligo)alkyl groups can be used for surface patterning in the nanometer regime and rings with extraannular oligostyryl groups are able to aggregate to supramolecular hollow polymer brushes.     

Annular tautomerism: experimental observations and quantum mechanics calculations

The use of MP2 level quantum mechanical (QM) calculations on isolated heteroaromatic ring systems for the prediction of the tautomeric propensities of whole molecules in a crystalline environment was examined. A Polarisable Continuum Model was used in the calculations to account for environment effects on the tautomeric relative stabilities. The calculated relative energies of tautomers were compared to relative abundances within the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB). The work was focussed on 84 annular tautomeric forms of 34 common ring systems. Good agreement was found between the calculations and the experimental data even if the quantity of these data was limited in many cases. The QM results were compared to those produced by much faster semiempirical calculations. In a search for other sources of the useful experimental data, the relative numbers of known compounds in which prototropic positions were often substituted by heavy atoms were also analysed. A scheme which groups all annular tautomeric transformations into 10 classes was developed. The scheme was designed to encompass a comprehensive set of known and theoretically possible tautomeric ring systems generated as part of a previous study. General trends across analogous ring systems were detected as a result. The calculations and statistics collected on crystallographic data as well as the general trends observed should be useful for the better modelling of annular tautomerism in the applications such as computer-aided drug design, small molecule crystal structure prediction, the naming of compounds and the interpretation of protein—small molecule crystal structures.     

Effects of substituents on synthetic analogs of chlorophylls. Part 2: Redox properties, optical spectra and electronic structure

The optical absorption spectra and redox properties are presented for 24 synthetic zinc chlorins and 18 free base analogs bearing a variety of 3,13 (beta) and 5,10,15 (meso) substituents. Results are also given for a zinc and free base oxophorbine, which contain the keto-bearing isocyclic ring present in the natural photosynthetic pigments such as chlorophyll a. Density functional theory calculations were carried out to probe the effects of the types and positions of substituents on the characteristics (energies, electron distributions) of the frontier molecular orbitals. A general finding is that the 3,13 positions are more sensitive to the effects of auxochromes than the 5,10,15 positions. The auxochromes investigated (acetyl>ethynyl>vinyl>aryl) cause a significant redshift and intensification of the Qy band upon placement at the 3,13 positions, whereas groups at the 5,10,15 positions result in much smaller redshifts that are accompanied by a decrease in relative Qy intensity. In addition, the substituent-induced shifts in first oxidation and reduction potentials faithfully track the energies of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The calculations show that the LUMO is shifted more by substituents than the HOMO, which derives from the differences in the electron densities of the two orbitals at the substituent sites. The trends in the substituent-induced effects on the wavelengths and relative intensities of the major features (By, Bx, Qx, Qy) in the near-UV to near-IR absorption bands are well accounted for using Gouterman's four-orbital model, which incorporates the effects of the substituents on the HOMO-1 and LUMO+1 in addition to the HOMO and LUMO. Collectively, the results and analysis presented herein and in the companion paper provide insights into the effects of substituents on the optical absorption, redox and other photophysical properties of the chlorins. These insights form a framework that underpins the rational design of chlorins for applications encompassing photomedicine and solar-energy conversion.     

15N NMR spectroscopy of some azines

¹⁵N NMR shielding data are presented for 56 cyclic azines in 0.5 M dimethyl sulfoxide solutions with 0.01 M increments of Cr(acac)₃ added for each nitrogen atom in the molecules. For the polyazines, the ¹⁵N signal assignments were based on ²J(NH) interactions and some INDO/S-SOS shielding calculations. The effects of α-, β- and γ-methyl and conjugated ring substitution on nitrogen shielding are presented and discussed, as are the influences arising from fusion with alicyclic and aromatic rings at various positions. The effects of a second nitrogen atom on the shielding of the first one are shown to be critically dependent on both their relative positions and on the position of fusion of conjugated ring systems.     

Modulation of Aggregation‐Induced Emission and Electroluminescence of Silole Derivatives by a Covalent Bonding Pattern

The deciphering of structure–property relationships is of high importance to rational design of functional molecules and to explore their potential applications. In this work, a series of silole derivatives substituted with benzo[b]thiophene (BT) at the 2,5‐positions of the silole ring are synthesized and characterized. The experimental investigation reveals that the covalent bonding through the 2‐position of BT (2‐BT) with silole ring allows a better conjugation of the backbone than that achieved though the 5‐position of BT (5‐BT), and results in totally different emission behaviors. The silole derivatives with 5‐BT groups are weakly fluorescent in solutions, but are induced to emit intensely in aggregates, presenting excellent aggregation‐induced emission (AIE) characteristics. Those with 2‐BT groups can fluoresce more strongly in solutions, but no obvious emission enhancements are found in aggregates, suggesting they are not AIE‐active. Theoretical calculations disclose that the good conjugation lowers the rotational motions of BT groups, which enables the molecules to emit more efficiently in solutions. But the well‐conjugated planar backbone is prone to form strong intermoelcular interactions in aggregates, which decreases the emission efficiency. Non‐doped organic light‐emitting diodes (OLEDs) are fabricated by using these siloles as emitters. AIE‐active silole derivatives show much better elecroluminescence properties than those without the AIE characterisic, demonstrating the advantage of AIE‐active emitters in OLED applications.     

Mass spectral fragmentations of cholesterol acetate oxidation products

In this work, electron-impact mass spectroscopy (EI-MS) was employed on a wide range of sterol compounds in order to study their behaviour with regard to their functional groups. In particular, some specific mechanisms of fragmentation occurring in these substrates (i.e. retro-Diels-Alder reaction, neutral molecules eliminations, specific hydrogen migrations) were investigated. Loss of the alkyl side chain and of the D ring were observed in all cases. Finally, a classification of sterols on the basis of characteristic mass spectral fragments is suggested, and further applications to substrates with functional groups on positions other than the A and B rings is proposed.     

Synthesis and mesophase behaviour of rigid rod‐like phenylthiophene‐based amphiphilic diol derivatives

Novel amphiphilic block molecules consisting of a rigid 2‐phenylthiophene or 5‐phenylbithienyl core, with a polar glycerol group attached to the phenyl ring and one or two alkyl chains attached to the thiophene ring on the other side, have been synthesised by using Ni(0) and Pd(0) catalyzed coupling reactions as key steps. The thermotropic and solvent‐induced liquid crystalline behaviour of these compounds was investigated by polarising optical microscopy and X‐ray diffraction. The influence of the length, number and position of the alkyl chains, and the length of the rigid core, on their mesophase behaviour was investigated. Compounds with one alkyl chain in the terminal 5‐position on the thiophene ring form only smectic A phases, compounds with two adjacent alkyl chains attached in the 4‐ and 5‐positions of the thiophene ring exhibit thermotropic columnar mesophases, and those with two long alkyl chains attached to the 3‐ and 5‐positions form columnar LC phases only in the presence of water. Another compound containing the longer 5‐phenylbithienyl core unit and two alkyl chains attached in lateral positions to each of the thiophene rings is not mesogenic.     

Interpretation of NMR spectra from four-membered rings

When as many as four vicinal couplings occur between four protons situated on three carbon atoms of a cyclobutane ring, one can employ the Karplus relation to assign the configuration of substituents at the remaining positions and make some inferences about the stereochemistry. Four examples are described; the spectra and data are analyzed.     

A quantum and deductive chemical study for all congeners of polybromo/chlorodibenzo-p-dioxin and polybromo/chlorodibenzofuran

We have performed semiempirical quantum chemical calculations to obtain the optimized structure and the free energy (DeltaG) for all congeners (1701) of polybromo/chlorodibenzo-p-dioxins, which include all the isomers of all the homologues, and those for (3321) polybromo/chlorodibenzofurans. Then, to apply the "Quantum and Deductive Chemistry Approach" on the dioxin chemistry, we have carried out the multiple linear regression (MLR) as functions of temperature and the substituted numbers and positions of chlorine and bromine. The optimized structure of dibenzo-p-dioxin and the dibenzofuran ring is significantly influenced by the substitutions of the peri and lateral halogen atoms. The bond length between the aromatic ring and halogen atom also is influenced by the neighboring atoms. The bromine substitution at the 2 and 8 positions of dibenzofuran reduces the steric repulsion between the chlorine atoms at the 1 and 9 positions. The coefficients of the predicting equation of DeltaG derived by MLR suggest that the probabilities of chlorine elimination from the peri and lateral positions for polychlorodibenzo-p-dioxin are nearly equal.     

Konformative Beweglichkeit Flexibler Ringsysteme–XI Untersuchungen mit Hilfe der Protonenresonanzspektroskopie Ringinversion bei Methyl- und Alkoxylcyclohexanen

The ring inversion of cyclohexane derivatives with one, two and three pairs of geminal methyl and alkoxyl groups has been studied by investigations of the temperature dependence of the NMR signals. The rate of the inversion depends on the number and the relative positions of the ligand pairs as well as on their size. A single pair of geminal ligands has only a very slight effect on the inversion rate. Two ligand pairs hinder the inversion when they are in the 1 and 4 positions relative to one another, but facilitate it when they are in the 1 and 3 positions. In both cases the effects are smaller with methoxyl groups than with methyl groups. Three ligand pairs significantly increase the inversion rate when they are in the 1, 3 and 5 positions, but reduce it when they are in the 1, 2 and 4 positions. The effect of 1,3 substituents is attributed to an increase in the energy of the ground state of the molecules whereas the effect of 1,4 arranged substituents is attributed to an increase in the energy of the transition state of the chair inversion.     

Convergence in [2+2+2] synthesis of β-phenylnaphthalene motif in polyaromatic natural products

Two optional routes to β-phenylnaphthalene structure are developed by introducing α- and β-styryl groups onto different positions in the benzocyclobutene ring followed by ring enlargement.