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Reversible Photochemistry, Absorption‐ and 1 H‐NMR.‐spectra, and oxidation of the [2,2]metacyclophane‐1‐ene ⇄ 4,5,15,16‐tetrahydropyrene system
Author(s) -
Naef R.,
Fischer Ernst
Publication year - 1974
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19740570739
Subject(s) - chemistry , molar absorptivity , spectral line , yield (engineering) , absorption (acoustics) , absorption spectroscopy , quantum yield , photochemistry , ene reaction , nmr spectra database , irradiation , proton nmr , extinction (optical mineralogy) , analytical chemistry (journal) , stereochemistry , organic chemistry , fluorescence , physics , mineralogy , quantum mechanics , astronomy , acoustics , nuclear physics , optics , materials science , metallurgy
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.