TY - JOUR A1 - John, Andreas A1 - Bock, Hans T1 - Elektronentransfer und Kontaktionen-Bildung, 42 [1,2]. Cyclovoltammetrische und ESR/ENDOR-Untersuchungen der Einelektronen-Reduktion von Diphenochinonen T1 - Electron transfer and contact ion pair formation, 42 [1,2]. Cyclovoltammetric and ESR/ENDOR investigations of the one-electron reduction of diphenoquinones T2 - Zeitschrift für Naturforschung, B N2 - Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations. In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives O=C(RC=CH)2C=C(HC=CR)2C=O with R = C(CH3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(tert-butyl)-substituted radical anion only adds Li⊕ and Na⊕, while K⊕ forms no ion pair. The 3,3ʹ,5,5ʹ-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me⊕, although Rb⊕ and Cs⊕ seem to be present solvent-separated in solution. The tetramethyl-substituted radical anion unfortunately polymerizes rapidly. Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation [Li⊕ M•⊖Li⊕]•⊕, or the difference in the coupling constants upon Me⊕ docking at one δ⊖O=C group, suggesting that about 87% of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion. Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural characterization should be attempted. KW - One-Electron Reduction of Diphenoquinones KW - Cyclovoltammetry KW - ESR/ENDOR Spectra KW - Contact Ion Pairs and Triples Y1 - 2014 UR - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/81534 UR - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-815341 SN - 1865-7117 SN - 0932-0776 VL - 50.1995 IS - 11 SP - 1699 EP - 1716 PB - Verlag der Zeitschrift für Naturforschung CY - Tübingen ER -