Search results for "Annulene"
showing 10 items of 34 documents
Inside Cover: An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird’s 4nπ-Electron Triplet Stabilization…
2015
Innentitelbild: An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird’s 4nπ-Electron Triplet Stabilizati…
2015
Areno-Condensed 1,7,13-Triaza[18]annulenes
2002
The 1,7,13-triaza[18]annulenes 9a−c were prepared by multi-step processes in which the final step consisted of a threefold cyclic condensation reaction of the Schiff bases 8a−c. Due to the length of the nine peripheral alkoxy chains, discotic liquid crystalline phases were obtained for 9b,c. The three nitrogen atoms in the central 18-membered ring not only permit protonation, but they can also serve for the complexation of NH4+ ions. The compounds 9a−c are highly photosensitive and exhibit crosslinking reactions on irradiation.
ChemInform Abstract: Synthesis and Photodimerization of Tetrabenzo[ab,f,jk,o][18]annulenes.
2010
ChemInform Abstract: Synthesis of Areno-Condensed [24]Annulenes.
2010
[24]Annulenes condensed with three phenanthrene units (11a−d) or with three chrysene ring systems (22) were prepared by multi-step syntheses. The cyclic condensation reaction in the final step led to highly symmetrical compounds. Long flexible alkoxy groups attached to the periphery enhance the solubility and give rise to a strong aggregation of the molecules which was observed in solution by NMR and fluorescence excitation spectroscopy, and in the pure state by the detection of liquid crystalline phases in differential scanning calorimetry and polarization microscopy.
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…
Doubly charged ions of bridged [4n] annulenes. An evaluation of diatropic ring current effects.
1985
Abstract [4n]Annulenes are transformed into doubly charged ions (dianion, dication) and characterized NMR spectroscopically. The diatropic character of the ionic (4n+2)π-systems is studied as a function of the number of π-electrons.
Synthesis of Areno-Condensed [24]Annulenes
2001
[24]Annulenes condensed with three phenanthrene units (11a−d) or with three chrysene ring systems (22) were prepared by multi-step syntheses. The cyclic condensation reaction in the final step led to highly symmetrical compounds. Long flexible alkoxy groups attached to the periphery enhance the solubility and give rise to a strong aggregation of the molecules which was observed in solution by NMR and fluorescence excitation spectroscopy, and in the pure state by the detection of liquid crystalline phases in differential scanning calorimetry and polarization microscopy.
Synthesis of Tripyreno[2,3,4-abc: 2,3,4-ghi: 2,3,4-mno][18]annulenes
2000
The title compounds were prepared in a multi-step synthesis in which primarily the pyrene building blocks were formed (1,2 11a,b). The final reaction step 11a,b 12a,b consisted of a threefold trans selective cyclocondensation process that generated the central 18-membered ring. Hexyloxy or dodecyloxy sidechains attached on the periphery led to the formation of liquid crystalline phases.
1H nmr chemical shifts of [14]annulenes and their dianion salts
1987
Abstract The bridged (14]annulene 2 was reduced into its dianion and the structure of the dianion salt was proven by chemical and spectroscopic means. The 1H NMR spectroscopic properties of 2 are similar to those of the structurally related bridged [14]annulene 1 , whereas the corresponding dianions 2 2- and 1 2- are strikingly different. The geometries of 1 and 2 and their dianions were studied by means of a modified π-SCF force field approach. Almost planar perimeters without significant bond length alternation are obtained for the neutral annulenes 1 and 2 , whereas their dianions are characterized by structures with reduced symmetry. The 1H chemical shifts of the bridged [14]annulenes a…