Which of the following structures represents the enol form that is a tautomer of the aldehyde ${\mathrm{CH}}_3\mathrm{CHO}$ (acetaldehyde)?

• A. ${\mathrm{CH}}_3\mathrm{CO}\mathrm{CH}3$
• B. ${\mathrm{CH}}_2=\mathrm{CH}\mathrm{OH}$
• C. ${\mathrm{CH}}_3\mathrm{COOH}$
• D. ${\mathrm{CH}}_3\mathrm{CH}2\mathrm{OH}$

Answer: (B)

Verified step by step guidance

1. Identify the given aldehyde: acetaldehyde, which has the structure \(\mathrm{CH_3CHO}\), where the carbonyl group (C=O) is attached to a methyl group.
2. Recall that keto-enol tautomerism involves the equilibrium between a keto form (containing a carbonyl group) and an enol form (containing an alkene \(\mathrm{C=C}\) and an alcohol \(\mathrm{-OH}\) group).
3. To find the enol tautomer of acetaldehyde, move a proton from the alpha carbon (the carbon adjacent to the carbonyl carbon) to the oxygen of the carbonyl group, and form a double bond between the alpha carbon and the carbonyl carbon.
4. Write the enol structure as \(\mathrm{CH_2=CHOH}\), where the double bond is between the first and second carbons, and the hydroxyl group is attached to the second carbon.
5. Compare the given options to this structure to identify the correct enol tautomer of acetaldehyde.