Which of the following statements is correct about methyl group?

  1. It stabilizes both carbocation and free radical equally.
  2. It stabilizes a free radical more than a carbocation.
  3. It stabilizes a carbocation more than a free radical.
  4. None of these.

I thought the answer would be (1). Keeping in mind these structures: The methyl group can stabilize the carbocation and the free radical group attached to it equally through hyperconjugation. However, the answer given is (3). How is this possible? Why is the carbocation more stable than the free radical? Are the structures I drew wrong?

  • $\begingroup$ Can you give an example where stabilization by radical formation is seen. $\endgroup$ Feb 27 '18 at 12:59
  • $\begingroup$ @AvatarShiny You'll have to scroll a bit and you will see free radical stabilization due to hyperconjugation. hubpages.com/education/Thorough-Chemistry-of-Hyperconjugation $\endgroup$
    – dr.drizzy
    Feb 27 '18 at 13:03
  • $\begingroup$ related chemistry.stackexchange.com/questions/64875/… $\endgroup$
    – Mithoron
    Feb 27 '18 at 20:31
  • 1
    $\begingroup$ @raajsuriya You can't draw a resonance structure involving all three hydrogen atoms on an adjacent methyl. They can't all be oriented properly for hyperconjugation at the same time. Let's just say that looking briefly at the linked web page, I'm not impressed. $\endgroup$
    – Zhe
    Feb 27 '18 at 22:52
  • $\begingroup$ @Zhe The link was not important I googled that quickly for Avtar Shiny. Do you know why carbocations are stabilized more than free radicals through hyperconjugation? Or is this something I should memorize? Thank you for your time $\endgroup$
    – dr.drizzy
    Feb 28 '18 at 5:48

A carbonation is deficient in 2 electrons whereas a free radical is only 1 electron deficient. Thus any type of stabilisation working on a carbonation will be much more effective as it is more electron deficient. Hence, hyperconjugation or inductive electron donation stabilises a carbocation more than it does a free radical.


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