Methyl Substitution as a Probe for π-Spin Distribution in the Radical Anion of 1,6-Methano[10]annulene

ESR. and ENDOR. spectra are reported for the radical anion of the 2-methyl derivative (III) of 1,6-methano10]annulene (I). Comparison of the hyperfine data for I·? and III·? with those for the radical anions of naphthalene (II) and its 1-methyl derivative (IV), respectively, confirms the suggestion that – despite the vastly different α-proton coupling constants – the π-spin distributions should be similar in the two series. This result provides further support for the view that the π-spin distribution, in particular, and the cyclic π-delocalisation, in general, are not seriously perturbed by moderate deviations of the π-perimeter from planarity.