The increasing order of stability of the following free...

The increasing order of stability of the following free radicals is (a) $\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \dot{\mathrm{C}} \cdot \mathrm{C}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}$ (b) $\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \mathrm{C} \mathrm{H}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}$ (c) $\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \mathrm{CH}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}$ (d) $\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \mathrm{CH}$

The increasing order of stability of the following free radicals is
(a) $\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \dot{\mathrm{C}} \cdot \mathrm{C}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}$
(b) $\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \mathrm{C} \mathrm{H}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}$
(c) $\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \mathrm{CH}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}$
(d) $\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}<\left(\mathrm{CH}_{3}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{3} \dot{\mathrm{C}}<\left(\mathrm{C}_{6} \mathrm{H}_{5}\right)_{2} \mathrm{CH}$

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Key Concepts

Resonance Stabilization

Resonance stabilization involves the delocalization of the unpaired electron across a conjugated system such as an aromatic ring. This spreading of electron density over multiple atoms reduces the electron's localized reactivity, making the radical more stable.

Free Radical Stability

Free radical stability refers to the inherent ability of a radical species to delocalize or mitigate the energy of its unpaired electron. Factors such as the number and type of substituents, the possibility of hyperconjugation, and resonance stabilization contribute to how easily a free radical stabilizes its electron deficiency.

Hyperconjugation

Hyperconjugation is the stabilization arising from the interaction of the electrons in sigma bonds (typically C–H or C–C bonds) with an adjacent empty or half-filled p-orbital of the radical center. This electron donation helps to disperse the radical character and lower the overall energy of the molecule.

Substituent Effects

Substituent effects encompass the influence of attached groups (either alkyl or aryl) on radical stability. Electron-donating groups can enhance stability through hyperconjugation and inductive effects, while groups capable of resonance donation, particularly aromatic rings, offer even greater stabilization by delocalizing the unpaired electron.

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