Which one of the following free radical is most stable:
Correct answer: C. (CH3)3C*
- A. CH3*
- B. (CH3)2CH*
- C. (CH3)3C*
- D. C2HS*
Explanation
Attachment of the alkyl group increases the stability of free radicals as alkyl groups are electron donating through the hyperconjugation effect, which is the electron density of C-C or C-H σ bond overlap with the half-filled p orbital of carbon radicals. Similar to carbocation, the carbon radical is also an electron-deficient species, so the electron-donating effect of alkyl groups helps stabilize it. With more alkyl groups involved, the radical is more stable.
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About Free Radical Substitution
Free radical substitution explains how alkanes react with halogens under ultraviolet light or heat through initiation, propagation and termination steps. The mechanism involves homolytic bond fission and radical intermediates, while product formation depends on the relative stability of radicals and differs from ionic substitution.
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