Question

An organic compound (X) has the molecular formula \(C_5H_{10}O\). Draw structures for (X) if it:
(I) does not give Tollen's test but gives a positive iodoform test.
(II) does not give Tollen's test and iodoform test but undergoes Aldol condensation.
(III) undergoes Cannizzaro's reaction.

Hint:

To quickly identify iodoform-positive ketones, look for a \(CH_3\) group directly attached to the carbonyl carbon (\(C=O\)).

Answer 1

Step 1: Understanding the Concept:
The molecular formula \(C_5H_{10}O\) corresponds to either an aldehyde or a ketone (General formula \(C_nH_{2n}O\)).
- Tollen's test is positive for aldehydes and negative for ketones.
- Iodoform test is positive for compounds containing the methyl keto group (\(CH_3-CO-\)).
- Aldol condensation requires \(\alpha\)-hydrogen atoms.
- Cannizzaro reaction is given by aldehydes with no \(\alpha\)-hydrogen atoms.
Step 2: Detailed Explanation:
(I) Compound does not give Tollen's test \(\implies\) it is a ketone. It gives a positive iodoform test \(\implies\) it is a methyl ketone. For 5 carbons, the only methyl ketone is Pentan-2-one.
Structure: \(CH_3-CO-CH_2-CH_2-CH_3\)
(II) Compound does not give Tollen's test \(\implies\) ketone. Does not give iodoform test \(\implies\) not a methyl ketone. Undergoes Aldol condensation \(\implies\) must have \(\alpha\)-hydrogens. For 5 carbons, this is Pentan-3-one.
Structure: \(CH_3-CH_2-CO-CH_2-CH_3\)
(III) Undergoes Cannizzaro reaction \(\implies\) it is an aldehyde with no \(\alpha\)-hydrogen. For 5 carbons, the structure is 2,2-Dimethylpropanal (also called Pivalaldehyde).
Structure: \((CH_3)_3C-CHO\)
Step 3: Final Answer:
The structures are Pentan-2-one for (I), Pentan-3-one for (II), and 2,2-Dimethylpropanal for (III).