What will be the product for the following reactions?
\(CH_3-X \overset{KCN}{\longrightarrow} A\)
\(CH_3-X \overset{AgNO_2}{\longrightarrow}B\)
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A: CH3CN; B: CH3NO2
Cyanide and nitrite ions are ambident nucleophiles: each can attack through two different atoms, and the reagent decides which one does.
KCN is predominantly ionic and gives free cyanide ions. They attack mainly through carbon, because a C–C bond is more stable than a C–N bond, so A is the alkyl cyanide (ethanenitrile):
\( \displaystyle \ce{CH3-X + KCN -> CH3CN + KX} \)
AgNO2 is covalent, and the nitrite group bonds through nitrogen, so B is the nitroalkane (nitromethane):
\( \displaystyle \ce{CH3-X + AgNO2 -> CH3NO2 + AgX} \)
Option (2) A: CH3NC; B: CH3–O–N=O — Incorrect. Both are the products of the other reagents: the isocyanide forms with covalent AgCN, and the alkyl nitrite forms with ionic \( \ce{KNO2} \) (attack through oxygen).
\( \displaystyle \ce{CH3-X + AgCN -> CH3NC + AgX} \)
\( \displaystyle \ce{CH3-X + KNO2 -> CH3-O-N=O + KX} \)
Option (3) A: CH3CN; B: CH3–O–N=O — Incorrect. A is right, but \( \ce{AgNO2} \) gives the nitroalkane (N-attack), not the alkyl nitrite (O-attack).
Option (4) A: CH3NC; B: CH3NO2 — Incorrect. B is right, but KCN gives the cyanide (C-attack), not the isocyanide.
NCERT (2026-27 edition):
Reactions of Haloalkanes – “… KCN is predominantly ionic and provides cyanide ions in solution. Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack takes place mainly through carbon atom and not through nitrogen atom since C—C bond is more stable than C—N bond. However, AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanide as the main product.”
Reactions of Haloalkanes – “… The linkage through oxygen results in alkyl nitrites while through nitrogen atom, it leads to nitroalkanes.”