Question

Which compound does not give HVZ reaction?
(A) ${ CH }_{ 3 }-{ CH }_{ 2 }-{ CH }_{ 2 }-{ COOH }$
(B)
(C)
(D)

Answer 1

Hint: HVZ stands for Hell-Volhard-Zelinsky halogenation reaction. The HVZ reaction is halogenation of carboxylic acids at alpha carbon.

Complete step by step solution:
> This reaction is generally carried out by treating carboxylic acids with halogen in the presence of red phosphorus and then works up with water.
> Those compounds which have alpha hydrogen show HVZ reaction while those which do not have alpha hydrogen do not show HVZ reaction.
- In this ${ CH }_{ 3 }-{ CH }_{ 2 }-{ CH }_{ 2 }-{ COOH }$ compound, alpha and beta hydrogen are present. That’s why butanoic acid shows a Hell-Volhard-Zelinsky halogenation reaction.
- In cyclohexyl carboxylic acid, alpha hydrogen is present as shown below,

So, this compound also shows the Hell-Volhard-Zelinsky halogenation reaction.

- In 1-methylcyclohexane-1-carboxylic acid, there is no alpha hydrogen present as the carbon is attached to 4 different bonds. So, this compound does not show the Hell-Volhard-Zelinsky halogenation reaction.
- In 2-cyclohexyl acetic acid, alpha hydrogen is present as shown in the figure;

Hence, this compound shows the HVZ reaction. The correct option is C.

Note: The possibility to make a mistake is that this reaction is specific for the replacement of alpha-hydrogens and not beta- hydrogens.