Hydrogen bond in the excited state of [2.2.2.2](1,2,4,5)cyclophane quinhydrones

Intra- and intermolecular hydrogen bond was studied in electron-donor-acceptor complexes in the excited state. It was shown that low-frequency shifts of electron-transfer bands are correlated with the strength of the hydrogen bond in the ground electron state. A satisfactory agreement was obtained between the results of quantum-chemical calculations of [2.2.2.2](1,2,4,5)cyclophane bisquinones and their reduced forms, [2.2.2.2] (1,2,4,5)cyclophane quinhydrones, with experimental data, and unusual physicochemical properties of quinhydrones are noted.     

A Triply [5]Helicene-Bridged (1,3,5)Cyclophane

A rigid propeller-shaped conjugated triple macrocycle consisting of two nearly perfectly stacked benzene rings and three linking [5]helicene moieties has been synthesized using a glyoxylic Perkin approach. Analysis of the electron delocalization in this atypical aromatic molecule revealed global aromaticity and a 78 π-electron circuit along the edge of its triple loop, to the detriment of the two 6 π-electron circuits in the two stacked benzene rings.     

Cyclization of (1,2,4,5-tetrazin-3-yl)hydrazones to 3,7-dihydro-1,2,4-triazolo[4,3-b]-1,2,4,5-tetrazines

The intramolecular cyclization of (6-R-1,2,4,5-tetrazin-3-yl)hydrazones of ketones (R is 3,5-dimethylpyrazol-1-yl, 4-methylimidazol-1-yl, or 2-alkylidenehydrazino) giving rise to the previously unknown 3,7-dihydro-1,2,4-triazolo[4,3-b]-1,2,4,5-tetrazines, including spiro compounds, was studied. The reactivity and the yields of the reaction products depend on the structure of the alkylidene fragment and the nature of the substituent in the tetrazine ring.

     

Correlated flipping of four benzene rings in substituted [2.2.2.2]Paracyclophanetetraenes

Dynamic NMR spectroscopy and molecular mechanics calculations show that the flipping of the four benzene binge in certain substituted [2.2.2.2]paracyclophanetetraenes occurs in a correlated fashion.     

Cyclophane,XIV : darstellung polymethylierter [2.2]paracyclophane

Starting from 4, 5, 12, 13-tetrakis(methoxycarbonyl)[2.2]paracyclophane ($\text{1}$), the penta-($\text{4}$), hexa-($\text{6a}$–$\text{c}$), hepta-($\text{7}$), and octamethyl-($\text{8}$) derivatives have been prepared by a repetitive formylation-reduction sequence.     

Temperature dependent chemical shift change in 4-substituted[2.2.2.2]paracyclophanes

Temperature dependent NMR spectra of 4-substituted tetrakis[2.2.2.2]paracyclophane (4°-PCP) were measured at low temperature. The high field shift at low temperature was remarkable for the protons meta and para to an electron withdrawing and/or bulky substituent. While the chemical shift change was very small for the aromatic protons of 4°-PCP bearing a not so bulky and electron donating substituent. From these observations it is concluded that the rotation or vibration of a benzene bearing an electron withdrawing and/or bulky substituent around C₂-C₃-C₆-C₉ axis was increasingly frozen as the temperature decreased to a more stable “lateral” (or half “lateral”, the intermediary state between “face” and “lateral”⁴) conformation, in an interesting contrast to the favored face conformation of unsubstituted 4°-PCP at low temperature as well as at room temperature.