Abstract The ESR.-spectra of the radical anions of 1, 6-methano-cyclodecapentaene (II) and of 1, 6-oxido-cyclodecapentaene (VII), as well as of some of their deutero-derivatives, are reported. The observed spin populations are in essential agreement with the predictions derived from a simple HMO-model, if the electron repelling effect of the bridging groups is included. The reduced width of the spectra may be due to direct leakage of the unpaired ...