IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

prem_1472

sir,

i am not able to solve yhe objectives in which stability of free radicals is asked.please,help me.

arvind1990

teritary>secondary>primary>CH₃!!

This is due to hyperconjugation.More the hyperconjugative structure,more is the stability!!Since tertiary has 9 hyerconjugative structure,more stable!!

The greater is the stability,more easily it is formed!!!

But allyl free radical and benzyl free radical are even more stable than tertiary due to resonance!!

iitkgp_bipin

Radical alkyl intermediates are stabilized by similar criteria as carbocations, the more substituted the radical center is, the more stable it is. This will direct their reactions: formation of a tertiary radical (R₃C·) is favored over secondary (R₂HC·) or primary (RH₂C·). However, radicals next to functional groups, such as carbonyl, nitrile, and ether are even more stable than tertiary alkyl radicals.

Radicals attack double bonds, but unlike similar ions, they are slightly less directed by electrostatic interactions. For example, the reactivity of nucleophilic ions with ?,?-unsaturated compounds (C=C-C=O) is directed by the electron-withdrawing effect of the oxygen, resulting in a partial positive charge on the carbonyl carbon. There are two reactions that are observed in the ionic case: the carbonyl is attacked in a direct addition to carbonyl, or the vinyl is attacked in conjugate addition, and in either case, the charge on the nucleophile is taken by the oxygen. Radicals add rapidly to the double bond, and the resulting ?-radical carbonyl is relatively stable.

khinart

See bro Free radicals are same as carbocations again stabilized ny hyper conjugation(Remember an alpha carbon can be a free radical also)Now if U have doubts in the mechanism there are 3 steps

1) Chain initiation

2)propagation

3)termination

These three steps are the only universal steps.In the first free radoicals are formed,in the second the reactions occur until one of the reactants stop and in the third free radical species combine to give compound.Rest U can go through NCERT

madhusudan.chavan

7969

Like carbocations, the imple alkyl free radicals follow the sequence tertiary>secondary>primary>methyl. This can be explained on the basis of hyperconjugation.

Triphenymethy>Diphenylmethyl>Benzyl>ally can be explained on the basis of resonance.

The overall order of stability is Benzyl>Allyl>Tert.butyl>isopropyl>Ethyl>methyl>phenyl>vinyl.

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