An ESR study of the conformation of the transient germanium-centred tris-(2-phenyl-2-methylpropyl)germyl radical

Abstract

ESR data are given for the tris-(2-phenyl-2-methylpropyl)germyl (trineophylgermyl) radical. At T > 60°C, the spectrum shows a septet due to the interaction of the unpaired electron with the six methylene protons, indicating their equivalence on the ESR time scale. As the temperature is lowered to −120°C an alternating linewidth effect is observed, indicating the inequivalence of the two protons of the methylene groups. This inequivalence shows that the radical has a pyramidal structure which is rigid on the ESR time scale at low temperatures. The exchange of the methylene protons between the two inequivalent positions is caused by hindered rotation around the CGe bonds. The preferred conformation of the radical has been determined and compared with those of similar tin-centred radicals. From the line broadening, an activation energy of 5.4 ± 0.8 kcal/mol for this exchange, and a lifetime of the conformation of 3.6 ± 0.3·10 −10 s at 23°C have been determined.