The stability of the free radicals allyl, benzyl, 3^∘, 2^∘, 1^∘ and CH3 is of the order (1) ally

step 1 The stability of the free radicals, allile, benzyl, 3 ,2, 2 ,0, 1 and CH3 is of the order. There

The stability of the free radicals allyl, benzyl, 3^∘, 2^∘,...

The stability of the free radicals allyl, benzyl, $3^{\circ}, 2^{\circ}$, $1^{\circ}$ and $\mathrm{CH}_{3}$ is of the order (1) allyl=benzyl $>3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}$ (2) allyl $>$ benzyl $>3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}$ (3) $3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}>$ allyl $>$ benzyl (4) $3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}>$ allyl=benzyl

The stability of the free radicals allyl, benzyl, $3^{\circ}, 2^{\circ}$, $1^{\circ}$ and $\mathrm{CH}_{3}$ is of the order
(1) allyl=benzyl $>3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}$
(2) allyl $>$ benzyl $>3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}$
(3) $3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}>$ allyl $>$ benzyl
(4) $3^{\circ}>2^{\circ}>1^{\circ}>\mathrm{CH}_{3}>$ allyl=benzyl

Key Concepts

Comparative Radical Stability

Comparative radical stability examines how different stabilization factors interact to determine the overall stability of various radicals. In many cases, radicals stabilized by resonance (like allyl and benzyl) are more stable than even tertiary radicals, which rely solely on hyperconjugation and inductive effects, establishing an order of stability that is crucial in predicting reactivity.

Substituent Effects

Substituent effects refer to how the nature and number of groups attached to the radical center influence its stability. Electron-donating groups increase the stability of radicals by providing additional electron density or through hyperconjugation, while resonance-capable substituents, as seen in allyl and benzyl radicals, can provide significant stabilization by delocalizing the unpaired electron.

Hyperconjugation

Hyperconjugation is the stabilization mechanism by which sigma bonds adjacent to a radical center interact with the empty or partially-filled p-orbital, dispersing the electron density. This effect is especially important in alkyl radicals, where more substituted radicals (such as tertiary) benefit from increased hyperconjugative interactions, making them more stable than secondary or primary radicals.

Resonance Stabilization

Resonance stabilization is the delocalization of an unpaired electron over two or more atoms through overlapping p-orbitals, which reduces the reactivity of a free radical. This concept is key for radicals like allyl and benzyl, where the charge can spread over multiple atoms, greatly enhancing stability compared to radicals that lack this delocalization.

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