Question

A carbonyl compound (A) of molecular weight 100 does not reduce Tollen's reagent but shows haloform reaction. On careful oxidation, (A) gives (B) an acid as one of the product with equivalent mass of 102. (B) when heated with sodalime yields 2-methylpropane. Which of the following is correct regarding structure of (A) and (B)?

• A. (A) : $(CH_3)_3CCOCH_3$
• B. (A) : $(CH_3)_2CHCH_2COCH_3$
• C. (B) : $(CH_3)_3CCOOH$
• D. (B) : $(CH_3)_2CHCH_2COOH$

Answer 1

Answer: (A), (C)

(A): $(CH_3)_3CCOCH_3$ and (B): $(CH_3)_3CCOOH

Answer 2

Here's the breakdown of why the correct structures are (A): $(CH_3)_3CCOCH_3$ and (B): $(CH_3)_3CCOOH$:

1. (A) is a methyl ketone: The compound (A) does not reduce Tollen's reagent, indicating it is a ketone. It also undergoes a haloform reaction, meaning it must be a methyl ketone (RCOCH₃).

2. Molecular Weight of (A): The molecular weight of (A) is 100. The structure $(CH_3)_3CCOCH_3$ fits this requirement.

3. Oxidation of (A) yields (B): Oxidation of the methyl ketone (A) yields a carboxylic acid (B) with a molecular weight of 102. The oxidation converts the $COCH_3$ group into $COOH$.

4. Structure of (B): The acid formed from $(CH_3)_3CCOCH_3$ would be $(CH_3)_3CCOOH$ (pivalic acid), which has a molecular weight of 102.

5. Decarboxylation of (B): Heating (B) with sodalime results in decarboxylation, yielding 2-methylpropane (isobutane). The reaction is: $(CH_3)_3CCOOH \xrightarrow{sodalime} (CH_3)_3CH$.

Therefore, the correct structures are (A): $(CH_3)_3CCOCH_3$ and (B): $(CH_3)_3CCOOH$.