The I-butylperoxyesters of 1-adamantyl, 1-bicyclo[2-2.2]octyl, and 1-norbornyl carboxylic acids thermally undergo first order, free radical decomposition in cumene with relative rate constants at 80' of 1 .O, 0.07, and 0.001 respectively. As measures of the stability of the derived bridgehead free radicals, the rates span a range much narrower than that for carbonium ion formation at these strained positions. The results are consistent with suggestions that free radicals have smaller force constants for out-of-plane bending than do the corresponding carbonium ions.

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