Predict the major product 'P' in the following sequence of reactions: (methylenecyclopentane bearing a CH3 group) (i) HBr, benzoy…

Question

Predict the major product 'P' in the following sequence of reactions: (methylenecyclopentane bearing a CH3 group) (i) HBr, benzoyl peroxide(ii) KCN(iii) Na(Hg)/C2H5OH P (Major).

1. A. Cyclopentane bearing a -CH3 and a -CH2NH2 group (on adjacent carbons) (Correct answer)
2. B. Cyclopentane bearing a -CH3 and a -CH2NH2 group (on the same carbon)
3. C. Cyclopentane bearing a -CH3 and a -NC (isocyanide) group
4. D. Cyclopentane bearing a -CH3 and a -NC group on the same carbon

Correct Answer

Option A — Cyclopentane bearing a -CH3 and a -CH2NH2 group (on adjacent carbons)

Detailed Solution & Explanation

The correct answer is Option 1 — the cyclopentane carrying $-$CH$_3$ and $-$CH$_2$NH$_2$.

Key Points

• Step (i) HBr with benzoyl peroxide gives anti-Markovnikov (peroxide/Kharasch) addition, placing Br on the terminal (less substituted) carbon of the exocyclic double bond.
• Step (ii) KCN performs nucleophilic substitution of Br by $-$CN, giving a nitrile ($-$CH$_2$CN).
• Step (iii) Na(Hg)/C$_2$H$_5$OH reduces the nitrile to a primary amine ($-$CH$_2$NH$_2$).
• The final major product P is the cyclopentane bearing $-$CH$_3$ and $-$CH$_2$NH$_2$.