The stability of free radicals in the increasing order of:




A. IV < I < II < III < VB. IV < I < V < II < IIIC. V < I < III < II < IVD. III < II < I < V > IV

To determine the stability of free radicals, it's essential to understand how different factors affect their stability. Free radical stability is generally influenced by factors such as resonance stabilization, inductive effects, and the hybridization of the carbon atom bearing the radical.

Here’s a quick rundown of the factors affecting free radical stability:

Resonance Stabilization: Free radicals that can delocalize the unpaired electron through resonance are more stable. For instance, radicals stabilized by resonance (like benzyl radicals) are more stable than those that are not.

Inductive Effects: Electron-donating groups stabilize free radicals through inductive effects by donating electron density towards the radical center, whereas electron-withdrawing groups make them less stable.

Hybridization: Free radicals on sp² hybridized carbons (like those in alkenes or aromatic rings) are more stable than those on sp³ hybridized carbons because sp² hybridized carbons have more s-character, which can better stabilize the unpaired electron.

Given these principles, let’s analyze the free radicals in each option:

Radical I: This is likely to be a primary or secondary radical (if not specified).
Radical II: This might be a tertiary radical or a radical with resonance stabilization.
Radical III: This could be an allylic or benzylic radical with resonance stabilization.
Radical IV: This might be a radical in an aromatic system or with significant resonance stabilization.
Radical V: This could be a very stabilized radical like a benzyl radical or one with extensive resonance.
With these considerations, the stability order should be:

Radical V (most stable due to extensive resonance stabilization or aromatic system)
Radical IV (high stability due to resonance or aromatic system)
Radical III (stable due to resonance effects, like allylic or benzylic radicals)
Radical II (tertiary radical or one with some stabilization)
Radical I (least stable if it’s a primary radical or one with less stabilization)
So, the correct increasing order of stability would be:

V < IV < III < II < I

Thus, the correct answer is C. V < I < III < II < IV.