Question

Free radicals can undergo (1) Disproportion to two species (2) Rearrangement to more stable free radical (3) Decomposition to give another free radical (4) Combination with other free radical (5) All are correct

Short answer

All are correct.

Step-by-step solution

Understanding Disproportionation

Disproportionation involves the transformation of two free radicals into two different chemical species. This typically results in one species being oxidized and the other being reduced.

Understanding Rearrangement

Rearrangement refers to the reorganization of the molecular structure of a free radical to form a more stable configuration. This often involves the migration of atoms or groups within the molecule.

Understanding Decomposition

Decomposition of free radicals occurs when a free radical breaks down to produce another free radical and other products. This process usually involves the cleavage of chemical bonds.

Understanding Combination

Combination occurs when two free radicals react together to form a single, more stable molecule. This neutralizes the unpaired electrons of both radicals.

Conclusion

Free radicals can undergo disproportionation, rearrangement, decomposition, and combination. Therefore, all the options listed are correct mechanisms.

Key concepts

Disproportionation

Disproportionation is a type of redox reaction where one molecule undergoes simultaneous oxidation and reduction. In the context of free radicals, it refers to the transformation of two free radicals into two distinct chemical species. This process often yields one oxidized and one reduced product.

For example, when two molecules of phosphorous trihydride (PH₃) react, we can see:
\[ 2PH_3 \rightarrow P_2H_4 + H_2 \text{ } \text{(disproportionation reaction)} \]
In this reaction, one PH₃ molecule is reduced to H₂, while the other is oxidized to P₂H₄. This shows how two radicals can stabilize by disproportionating into different products.

Rearrangement

Rearrangement in free radical chemistry refers to the process where the molecular structure of a free radical changes to a more stable form. This often involves the movement of atoms or groups within the molecule.

Consider the free radical formed during the reaction of isobutane with a halogen:
\[ (\text{CH}_3)_3 \text{C} \bullet \rightarrow (\text{CH}_3)_2 \text{C} \bullet \text{CH}_2\text{ } (\text{rearrangement}) \]
Here, the tertiary butyl radical rearranges to a more stable secondary butyl radical, making the overall system more stable. This rearrangement lowers the energy of the molecule and results in a more stable free radical.

Decomposition

Decomposition in the context of free radicals refers to the process where a free radical breaks down to form another free radical and other products. This typically involves the breaking of chemical bonds.

For example, consider the decomposition of benzoyl peroxide (C₆H₅CO-OO-COC₆H₅):
\[ \text{C}_6\text{H}_5\text{CO-OO-COC}_6\text{H}_5 \rightarrow 2\text{C}_6\text{H}_5\text{CO}-\bullet + \text{O}_2 \text{ } (\text{decomposition}) \]
In this reaction, benzoyl peroxide decomposes to produce two benzoyl radicals and molecular oxygen. This illustrates how free radicals can form new radicals through decomposition.

Combination Reactions

Combination reactions involving free radicals occur when two radicals come together to form a more stable molecule, effectively neutralizing each other. This is important because it helps to terminate chain reactions in radical chemistry.

Consider the reaction between two methyl radicals:
\[ \text{2CH}_3\bullet \rightarrow \text{CH}_3\text{CH}_3 \text{ } (\text{combination reaction}) \]
Here, two methyl radicals combine to form ethane (C₂H₆), a more stable molecule. This reaction demonstrates how free radicals decrease their reactivity by forming a stable bond through combination.