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Which of the following compounds or reactions is correctly matched with the named reaction? (1) HCHO (formaldehyde) - Cannizzaro reaction (2) OCH2-CHO (glycolaldehyde) - haloform reaction (3) Cyclohexanone - Wolff-Kishner reduction (4) Vicinal dihalide on heating gives ethene - dehydrohalogenation

1. (1) HCHO - Cannizzaro reaction
2. (2) OCH2-CHO - haloform reaction
3. (3) Cyclohexanone - Wolff-Kishner reduction
4. (4) Vicinal dihalide on heating gives ethene

Correct answer: (1) HCHO - Cannizzaro reaction

Solution

Option 1: HCHO (formaldehyde) has no alpha-hydrogen => undergoes Cannizzaro reaction in conc. NaOH (disproportionation to methanol + formate). CORRECT. Option 2: OCH2-CHO is glycolaldehyde - it lacks the CH3CO- group needed for haloform reaction, so this is INCORRECT. Option 3: Cyclohexanone reduced by Wolff-Kishner would give cyclohexane, not cyclohexene. The reaction is valid but the product shown (cyclohexane) would be correct - need to see exact option. Option 4: Vicinal dihalide on heating with KOH/alc gives alkene - this is also correct chemistry but description may be incomplete (needs base, not just heating). Option 1 is most clearly and unambiguously correct.

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