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Reversible Photochemistry, Absorption- and 1H-NMR.-spectra, and oxidation of the [2,2]metacyclophane-1-ene ⇄ 4,5,15,16-tetrahydropyrene system

✍ Scribed by R. Naef; Ernst Fischer

Publisher
John Wiley and Sons
Year
1974
Tongue
German
Weight
559 KB
Volume
57
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The reversible photointerconversion in the above system was investigated in a wide range of temperatures and wavelengths of irradiation. The tetrahydropyrenes are obtainable only photochemically. The unmethylated and the mono‐methylated compound are oxidized with iodine quantitatively to 4,5‐dihydropyrene, even at −30°. This makes it possible to estimate the absolute concentration of the tetrahydropyrenes, and thereby their molar extinction coefficients and complete electronic absorption spectra. The quantum yields in both directions do not vary appreciably with the temperature, down to −190°. This is the first case in which the photocyclization yield of a cis‐stilbenelike compound is not attenuated on cooling, and reflects the special character of highly constrained structures. No emission was observed in solution. ^1^H‐NMR.‐spectra of both modifications of the dimethylated compound were taken. They support the structures assumed for both modifications, and also allow an estimate of their relative concentrations.

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