Match List I with List II
| List I | List II |
| A. \(CH_3CH_2Br\, \ +\, \ alc. KOH\) | I. \(CH_3CH_2NO_2\) |
| B. \(CH_3CH_2Br\, \ +\, \ aq. KOH\) | II. \(CH_2=CH_2\) |
| C. \(CH_3CH_2Br\, \ +\, \ KNO_2\) | III. \(CH_3CH_2ONO\) |
| D. \(CH_3CH_2Br\, \ +\, \ AgNO_2\) | IV. \(CH_3CH_2OH\) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-II, B-IV, C-III, D-I
The same bromoethane gives different products with different reagents. In alcoholic KOH, elimination is favoured; in aqueous KOH, substitution by \( \ce{OH-} \). The nitrite ion is an ambident nucleophile: ionic \( \ce{KNO2} \) attacks through oxygen, while covalent \( \ce{AgNO2} \) attacks through nitrogen.
(A) CH3CH2Br + alc. KOH — This matches (II) CH2=CH2. On heating, H from the β-carbon and Br from the α-carbon are removed (dehydrohalogenation).
\( \displaystyle \ce{CH3CH2Br} \xrightarrow[\Delta]{\text{alc. }\ce{KOH}} \ce{CH2=CH2 + KBr + H2O} \)
(B) CH3CH2Br + aq. KOH — This matches (IV) CH3CH2OH. The \( \ce{OH-} \) ion replaces Br (nucleophilic substitution).
\( \displaystyle \ce{CH3CH2Br} \xrightarrow{\text{aq. }\ce{KOH}} \ce{CH3CH2OH + KBr} \)
(C) CH3CH2Br + KNO2 — This matches (III) CH3CH2ONO. The free nitrite ion attacks through oxygen, giving ethyl nitrite.
\( \displaystyle \ce{CH3CH2Br + KNO2 -> CH3CH2-O-N=O + KBr} \)
(D) CH3CH2Br + AgNO2 — This matches (I) CH3CH2NO2. In covalent \( \ce{AgNO2} \) the lone pair on nitrogen attacks, giving nitroethane.
\( \displaystyle \ce{CH3CH2Br + AgNO2 -> CH3CH2NO2 + AgBr} \)
NCERT (2026-27 edition):
Nucleophilic Substitution of Alkyl Halides (R–X) (rows of Table 6.4)
| Reagent | Nucleophile (Nu−) | Substitution product R–Nu | Class of main product |
|---|---|---|---|
| NaOH (KOH) | HO− | ROH | Alcohol |
| KNO2 | O=N—O− | R—O—N=O | Alkyl nitrite |
| AgNO2 | Ag—Ö—N=O | R—NO2 | Nitroalkane |
Elimination Reactions – “When a haloalkane with β-hydrogen atom is heated with alcoholic solution of potassium hydroxide, there is elimination of hydrogen atom from β-carbon and a halogen atom from the α-carbon atom.”