Summury. SSR. spectra of the radical anions of 1,6-methano[lO]annulcnc (1) and its 2,5,7, 0tetradeuterio derivative I1 are reported for a temperature range of over 100". The abnormally small magnitudes of the a-proton coupling constants are attributed to thc deviation of the ten-Inernbered n-perimeter from planarity; an cxtension of the McConneZZ equation is proposed to achieve agreement between theory and experiment. It is suggested that the marked temperaturedependence of the ESR. spectra arises from slight changes in geometry which for Ie should have a more pronounced cffect on the a-proton coupling constants than for planar n-radicals.Several years ago, we reported the ESR. data for the radical anions of 3,6methano[lO]annulene (I) and some of this deuterio derivatives [l]. The coupling constants of the cl-protons3) in 10 were found to deviate strongly from the expected values. Later investigations also revealed that the ESR. spectrum of 10, which was previously observed at -70", is markedly temperature dependent.In the present paper we report the ESR. data for 10 and its 2,5,7,10-tetradeuterio derivative 110 over a range of more than 100°C.4) We also discuss the effect of nonplanarity of the ten-membered perimeter on the a-proton coupling constants and attempt to rationalize their temperature dependence in terms of changes in geometry.Results. -Radical anion of l,6-methano[10]annulene (I). Fig. 1 illustrates the effect of temperature variation on the ESR. spectra of IQ in 1,2-dimethoxyethane (DME) with Na@ as counter-ion.5) Before the observed changes in the spectra are l)