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

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.
Solution:
(I) Compound (X) that gives a positive iodoform test but does not give Tollen's test:
The iodoform test is positive for compounds that have a methyl group attached to a carbonyl group (such as methyl ketones). Since the compound does not give a Tollen's test, it cannot be an aldehyde but could be a methyl ketone.
Therefore, the structure of \(X\) is 3-pentanone, which has the formula \(C_5H_{10}O\).
The structure is:
\[ \text{CH}_3\text{COCH}_2\text{CH}_2\text{CH}_3 \] (II) Compound (X) that does not give Tollen's test or iodoform test but undergoes Aldol condensation:
Aldol condensation occurs with aldehydes or ketones that have at least one \(\alpha\)-hydrogen. The compound must be a carbonyl compound that is capable of undergoing self-condensation.
Since it doesn't give the iodoform test or Tollen's test, it is not a methyl ketone or an aldehyde. A possible structure could be butan-2-one, which can undergo Aldol condensation.
The structure is:
\[ \text{CH}_3\text{COCH}_2\text{CH}_3 \] (III) Compound (X) that undergoes Cannizzaro's reaction:
The Cannizzaro reaction occurs with non-enolizable aldehydes, where one molecule of aldehyde undergoes reduction to form an alcohol and the other is oxidized to a carboxylic acid salt. Since \(X\) does not give Tollen's test, it is not an aldehyde with an \(\alpha\)-hydrogen. A possible compound is benzaldehyde, which undergoes the Cannizzaro reaction in the absence of \(\alpha\)-hydrogens.
The structure is:
\[ \text{C}_6\text{H}_5\text{CHO} \]