Which of the following compounds will give Hell-Volhard-Zelinsky reaction ?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → R – CH2 – COOH
In the Hell-Volhard-Zelinsky (HVZ) reaction, a carboxylic acid that has an α-hydrogen is halogenated at the α-carbon when it is treated with chlorine or bromine in the presence of a small amount of red phosphorus:
\( \displaystyle \ce{R-CH2-COOH} \xrightarrow[\text{(ii) }\ce{H2O}]{\text{(i) }\ce{X2}/\text{red P}} \ce{R-CH(X)-COOH + HX} \)
The compound must therefore be a carboxylic acid with at least one α-hydrogen. \( \ce{R-CH2-COOH} \) has two α-hydrogens, so it gives the HVZ reaction.
Why the other options are incorrect
Option (2) R3C – CHO — Incorrect. It is an aldehyde, not a carboxylic acid, and its α-carbon carries no hydrogen at all; with concentrated alkali it gives the Cannizzaro reaction instead.
Option (3) R2CO — Incorrect. It is a ketone, not a carboxylic acid; ketones with α-hydrogens undergo other reactions such as aldol condensation.
Option (4) H – COOH — Incorrect. Formic acid is a carboxylic acid, but it has no α-carbon, so there is no α-hydrogen to replace.
NCERT (2026-27 edition):
Substitution Reactions in the Hydrocarbon Part
