Question

Iodoform reaction with sodium hypoiodite is used for detection of .

• A. \(\text{CH}_3\text{CO}\) group
• B. \(\text{CH}_3\text{CO}\) and \(\text{CH}_3\text{CH(OH)}\) groups
• C. \(\text{CH}_3\text{O}\) group
• D. \((\text{CH}_3)_3\text{CO}\) group

Hint:

Iodoform test (\(\text{I}_2 + \text{NaOH}\)) gives a positive yellow precipitate of \(\text{CHI}_3\) (mp \(119^\circ\text{C}\)) with:
1. \(\text{CH}_3-\text{C}=\text{O}\) (e.g., acetaldehyde, all methyl ketones).
2. \(\text{CH}_3-\text{CH(OH)}-\) (e.g., ethanol, secondary alcohols with a methyl group).

Answer 1

The Correct Option is B

Concept:
The iodoform test is used to detect methyl ketones and secondary alcohols containing the \(\text{CH}_3\text{CH(OH)}-\) group. 
When these compounds are treated with iodine and sodium hydroxide, they produce a yellow precipitate of iodoform, \(\text{CHI}_3\). 

Step 1: Reaction of Methyl Ketones: 
Compounds containing the \(\text{CH}_3\text{CO}-\) group undergo the iodoform reaction. 
The methyl group adjacent to the carbonyl group undergoes successive iodination to form a triiodomethyl carbonyl compound. 
\[ \text{RCOCH}_3 + 3\text{I}_2 + 3\text{NaOH} \rightarrow \text{RCOCI}_3 + 3\text{NaI} + 3\text{H}_2\text{O} \] The intermediate then reacts with sodium hydroxide to form a carboxylate salt and yellow iodoform precipitate. 
\[ \text{RCOCI}_3 + \text{NaOH} \rightarrow \text{RCOONa} + \text{CHI}_3\downarrow \] 
Step 2: Reaction of Secondary Alcohols: 
Compounds containing the \(\text{CH}_3\text{CH(OH)}-\) group also give the iodoform test. 
These alcohols are first oxidized to the corresponding methyl ketones. 
\[ \text{RCH(OH)CH}_3 \xrightarrow{[\text{O}]} \text{RCOCH}_3 \] The methyl ketone formed then undergoes the iodoform reaction and produces yellow \(\text{CHI}_3\). 

Step 3: Groups That Do Not Give the Iodoform Test: 
Groups such as \(\text{CH}_3\text{O}-\) and \((\text{CH}_3)_3\text{CO}-\) do not form methyl ketones under the reaction conditions. 
Therefore, they do not give the iodoform test. 

Final Answer: 
Thus, the iodoform test is given by compounds containing \(\text{CH}_3\text{CO}-\) and \(\text{CH}_3\text{CH(OH)}-\) groups. 
\[ \boxed{\text{Option (B)}} \]