Radicals, reduction rotation barrier

The experimental result seems to support this model. Table 11 lists values for rotational barriers in some allyl radicals (Sustmann, 1986). It includes the rotational barrier in the isomeric 1-cyano-l-methoxyallyl radicals [32]/ [33] (Korth et al., 1984). In order to see whether the magnitude of the rotational barriers discloses a special captodative effect it is necessary to compare the monocaptor and donor-substituted radicals with disubstituted analogues. As is expected on the basis of the general influence of substituents on radical centres, both captor and donor substituents lower the rotational barrier, the captor substituent to a greater extent. Disubstitution by the same substituent, i.e. dicaptor- and didonor-substituted systems, do not even show additivity in the reduction of the rotational barrier. This phenomenon appears to be a general one and has led to the conclusion that additivity of substituent effects is already a manifestation of a special behaviour, viz., of a captodative effect. The barrier in the 1-cyano-l-methoxyallyl radicals [32]/... 

Of other substances containing the furan ring in an otherwise hydrocarbon molecular environment, 5 forms an anion-radical on reduction with potassium. This radical has been the subject of a solution ESR and ENDOR study by Gerson and co-workers. Spin distribution, ion-pairing effects, and barriers to rotation of the phenylene groups were investigated. As implied earlier in the discussion of ECL, isobenzofurans and tetraphenylfuran also form anion-radicals. " ... 

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