Read the following passage and answer questions.
Nucleophiles attack at that part of the substrate molecule which is electron deficient. The reaction in which a nucleophile replaces already existing nucleophile in a molecule is called nucleophilic substitution reaction. Haloalkanes are substrates in these reactions. In this type of reaction, a nucleophile reacts with haloalkane (the substrate) having a partial positive charge on the carbon atom bonded to halogen. A substitution reaction takes place and halogen atom, called leaving group departs as halide ion. Since the substitution reaction is initiated by a nucleophile, it is called nucleophilic substitution reaction.
When $KNO_2$ reacts with R-X, what is the major product?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Alkyl nitrite
When potassium nitrite (KNO₂) reacts with an alkyl halide (R–X), the reaction typically gives a mixture of two products:
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Nitroalkane (R–NO₂)
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Alkyl nitrite (R–O–NO)
However, the major product depends on the metal:
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With KNO₂, the major product is alkyl nitrite (R–O–NO)
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With AgNO₂, the major product is nitroalkane (R–NO₂)
This difference arises due to the nucleophilicity of the nitrite ion (NO₂⁻), which is ambident (can attack via N or O):
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K⁺NO₂⁻ → O-attack (→ R–O–NO) → Alkyl nitrite (major)
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Ag⁺NO₂⁻ → N-attack (→ R–NO₂) → Nitroalkane (major)