Ethyl radical pyramidalization

Figure 4.10 Stabilization of ethyl radical through pyramidalization.

Stabilization of ethyl radical through pyramidalization. (Adapted from reference 68.)... 

For ethyl and isopropyl the effect is not large. Theory predicts, however, that the f-butyl is substantially pyramidalized, with a C-C-C angle of 117.3°. For f-butyl and the other alkyl radicals, the barrier to pyramidal inversion is quite small. One measurement suggests a barrier of roughly 0.45 kcal / mol for t-butyl radical. So, under most experimental conditions, simple alkyl radicals can be... 

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