Search results for "Aromaticity"
showing 10 items of 138 documents
Molecule Isomerism Modulates the Diradical Properties of Stable Singlet Diradicaloids
2019
Inclusion of quinoidal cores in conjugated hydrocarbons is a common strategy to modulate the properties of diradicaloids formed by aromaticity recovery within the quinoidal unit. Here we describe an alternative approach of tuning of diradical properties in indenoindenodibenzothiophenes upon anti → syn isomerism of the benzothiophene motif. This alters the relationship of the S atom with the radical center from linear to cross conjugation yet retains the same 2,6-naphtho conjugation pattern of the rearomatized core. We conduct a full comparison between the anti and syn derivatives based on structural, spectroscopic, theoretical, and magnetic measurements, showing that these systems are stabl…
A Tale of Two Isomers: Enhanced Antiaromaticity/Diradical Character versus Deleterious Ring‐Opening of Benzofuran‐fused s ‐Indacenes and Dicyclopenta…
2021
We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF. syn-IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF. In the case of the anti-isomers, synthesized via 2-substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All th…
On-Surface Synthesis of Unsaturated Carbon Nanostructures with Regularly Fused Pentagon–Heptagon Pairs
2020
Multiple fused pentagon-heptagon pairs are frequently found as defects at the grain boundaries of the hexagonal graphene lattice and are suggested to have a fundamental influence on graphene-related materials. However, the construction of sp2-carbon skeletons with multiple regularly fused pentagon-heptagon pairs is challenging. In this work, we found that the pentagon-heptagon skeleton of azulene was rearranged during the thermal reaction of an azulene-incorporated organometallic polymer on Au(111). The resulting sp2-carbon frameworks were characterized by high-resolution scanning probe microscopy techniques and feature novel polycyclic architectures composed of multiple regularly fused pen…
Poly(amine) biphenyl derivatives as fluorescent sensors for anions and cations
2005
Four new ligands, derived from tetramethylbenzidine and containing additional amino groups, are described. The influence of pH on the fluorescent properties of these ligands has been studied, and the effect of the dihedral angle between the aromatic rings on the fluorescent response has been established. The behaviour of the new ligands, and that of others previously described in both the complexation and sensing of different anions and cations, are also described.
π-Ring currents in doped coronenes with nitrogen and boron: diatropic-paratropic duality.
2015
The change in the electronic structure of coronene upon doping with nitrogen or boron has been theoretically studied by means of its magnetic properties and magnetic field induced current density maps. The addition of two atoms of nitrogen or boron to the central ring of coronene causes a drastic variation in the delocalization of π-electrons, which does not depend on its nature but instead on its position. Then, doping in the para position makes coronene more aromatic while doping in the meta position makes it to become antiaromatic. The magnetic behavior of the pristine molecule is characterized by two concentric currents flowing in opposite senses that are converted into hemi-perimetric …
Tautomeric preferences of phthalones and related compounds
2007
Abstract Multinuclear magnetic resonance and IR spectra prove that although 2-(diacylmethyl)pyridines and 2-(diacylmethyl)quinolines are β-diketones, their proton transfer product present in chloroform solution is not ketoenol but enaminone (earlier opinions were contradictory). Quinoline derivatives are less zwitterionic by character than the respective pyridyl congeners. The β-diketone form itself may also be rarely present in the solution. X-ray data show that 2-(2(1H)-pyridinylidene)-1H-indene-1,3(2H)-dione, i.e., enaminone tautomer of 2-(pyridin-2-yl)-2H-indene-1,3-dione, is also the only form present in crystal. Ab initio calculations show that the enaminone is usually more stable tha…
Thermal degradation of novolac resins by pyrolysis-gas chromatography with a movable reaction zone
1999
Abstract A previously described, a pyrolysis device with a movable reaction zone was used in the present work for thermal degradation of novolac resins. The products of thermal reactions were analysed by pyrolysis–GC. Owing to the heating of reaction zone to the maximal temperature of the chromatographic column, the high boiling pyrolysis products could be analysed. Bisphenols and trisphenols with aromatic rings coupled by methylene bridges and its methyl derivatives have been found among the compounds. The structure of the heavy pyrolysis products has been confirmed using GC–MS.
ChemInform Abstract: Areno-Condensed Annulenes - Extended Discotic Mesogens.
2010
[n]Annulenes (n ≥12) condensed with 2-4 aromatic ring systems (benzenes, naphthalenes, anthracenes, phenanthrenes, chrysenes, pyrenes) can be prepared by cyclocondensation reactions or ring transformations. Due to the local arene aromaticity, the molecules can be regarded as aromatic islands, which are connected by olefinic bridges. The compounds are non-planar, but the majority of the systems shows a fast inversion of the central macrocyclic ring, so that the molecules appear on average as large planar discs, which consist of extended π systems. The aggregation tendency (π stacking) of the compounds can be strengthened by the attachment of flexible saturated chains on the periphery. The di…
1-[4-(2-Aminoanilino)phenyl]-2,2,2-trifluoroethanone
2010
In the title compound, C14H11F3N2O, the two aromatic rings are oriented at a dihedral angle of 70.84 (8)°. The crystal structure displays intermolecular N—H...O and N—H...F interactions.
N-{2-Methyl-5-[(5-oxo-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-2-yl)amino]phenyl}benzamide
2010
In the title compound, C29H24N2O2, the two aromatic rings of the tricyclic unit are oriented at a dihedral angle of 32.27 (8)°. In the crystal N—H...O hydrogen bonds link the molecules into chains along the a axis. Further N—H...·O interactions link the chains.