Question

The compound(s) that shows(show) positive haloform test is(are) 

• A. (A)
• B. (B)
• C. (C)
• D. (D)

Hint:

In the haloform test, compounds with a –CH3 group adjacent to a carbonyl group, such as methyl ketones, give a positive result.

Answer 1

The Correct Option is A, B

The Requirement for a Positive Haloform Test

A compound gives a positive haloform test (reaction with $\text{X}_2$/$\text{OH}^-$ or $\text{I}_2$/$\text{NaOH}$, forming a haloform $\text{CHX}_3$) if it possesses one of the following structural units:

1. Methyl Ketone Group: A methyl ketone group ($R-\text{CO}-\text{CH}_3$), where $R$ can be alkyl, aryl, or $\text{H}$ (except for formic acid, which doesn't react). 
2. Secondary Alcohol with a Methyl Group: A secondary alcohol with a methyl group adjacent to the $\text{-OH}$ bearing carbon ($\text{R-CH(OH)-CH}_3$). These are oxidized to methyl ketones under the reaction conditions before reacting further.

Analysis of the Options

We analyze each compound for the presence of the $\text{R-CO-CH}_3$ group:

(A) $p$-Methylacetophenone:

$$\text{Compound (A)} = \text{Ar}-\text{CO}-\text{CH}_3$$

This compound has a methyl ketone ($\text{CO}-\text{CH}_3$) group.

Therefore, Compound (A) shows a positive haloform test.

(B) Benzylidineacetone (4-Phenylbut-3-en-2-one):

$$\text{Compound (B)} = \text{Ar}-\text{CH}=\text{CH}-\text{CO}-\text{CH}_3$$

This compound also has a methyl ketone ($\text{CO}-\text{CH}_3$) group.

Therefore, Compound (B) shows a positive haloform test.

(C) Methyl $p$-Toluate:

$$\text{Compound (C)} = \text{Ar}-\text{CO}-\text{OCH}_3$$

This is an ester. It does not possess the $\text{CO}-\text{CH}_3$ group directly attached to the carbonyl carbon.

Therefore, Compound (C) does not show a positive haloform test.

(D) $p$-Methylstyrene (1-Propenylbenzene):

$$\text{Compound (D)} = \text{Ar}-\text{CH}=\text{CH}-\text{CH}_3$$

This is an alkene. It is neither a methyl ketone nor the required secondary alcohol structure.

Therefore, Compound (D) does not show a positive haloform test.

Conclusion

The compounds that show a positive haloform test are (A) and (B).

The correct answer is (A) and (B).