Estimation of hyperfine coupling constants of29Si nuclei in the radical anions of trimethylsilyl-substituted π-electron systems

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Abstract
An attempt has been made to relate the coupling constant a Si of a 29Si nucleus in the radical anions of nine trimethylsilyl derivatives of π-electron systems to the spin populations ρ Si and of the silicon and the substituted carbon centre , respectively. For the parameter Q CSi of the relation an absolute value of circa 20 gauss is found, whereas Q Si appears not to be significantly different from zero. The coupling constants a Si calculated by means of this relation agree moderately well with the experimental values (standard error circa 0·6 gauss). An HMO model in which the trimethylsilyl substituents are treated as pseudo-π-centres, with the parameters h Si = -1·5 and k CSi = 0·55, reproduces satisfactorily the spin distribution in the corresponding radical anions.