The Radical Anions of [2.2.2.2]Paracyclophane-1,9,17,25-tetraene and Some of its Heteroaromatic Analogues

✍ Scribed by Fabian Gerson; Walter Huber; Olof Wennerström

• Publisher: John Wiley and Sons
• Year: 1978
• Tongue: German
• Weight: 549 KB
• Volume: 61
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19780610803

✦ Synopsis

Abstract

The radical anions of [2.2.2.2]paracyclophane‐ 1,9,17,25‐tetraene (I), [2] (2, 5)‐furano [2]paracyclo [2] (2,5)furano [2]paracyclophane‐1,8, 16,23‐tetraene (II), [2]‐(2,5)thiopheno [2]paracyclo [2] (2,5)thiopheno [2]paracyclophane‐1,8,16,23‐tetraene (III) and 2.2.2.2thiophenophane‐1,8,15,22‐tetraene (IV) have been studied by ESR. and ENDOR. spectroscopy. The assignment of the proton coupling constants, a~Hμ~ is to a large extent based on investigations of deuteriated derivatives. These investigations impressively demonstrate the potential of ENDOR. spectroscopy as an analytical tool. The Arrhenius activation energies, E~a~, for the rotation of phenylene fragments about the bonds linking them with the ethylenic parts in I⊖ and II⊖ are 36±6 and 28±4 kJ/mol, respectively. The value a~Hμ~ of the olefinic protons in I⊖ appears substantially smaller than expected for the corresponding planar radical anion. The hyperfine data for II⊖, III⊖ and IV⊖ are consistent with the conformations which should minimize the deviations of the macrocyclic π‐systems from planarity. In the case of II⊖, tight ion pairs are formed by the radical anion and its counter‐ion, K⊕, in DME, owing to the strong association of the alkali metal cation with one of the furan moieties. An analogous interaction of K⊕ with a thiophene moiety in III⊖ must be weaker, since no effects of ion pairing on the ESR. and ENDOR. spectra have been observed for this radical anion.