Which of the following compounds is an aldehyde?

• A. ${\mathrm{CH}}_3\mathrm{COCH}{3}_{}$
• B. ${\mathrm{CH}}_3\mathrm{COOH}$
• C. ${\mathrm{CH}}_3\mathrm{CH}{2}_{}\mathrm{OH}$
• D. ${\mathrm{CH}}_3\mathrm{CHO}$

Answer: (D)

Verified step by step guidance

1. Recall the definition of an aldehyde: it is an organic compound containing a carbonyl group (C=O) bonded to at least one hydrogen atom, typically represented as \$\mathrm{R{-}CHO}\$, where R is a carbon-containing group or hydrogen.
2. Examine each given compound's structure to identify the functional groups present. For example, look for the carbonyl group (C=O) and check what atoms or groups are attached to the carbonyl carbon.
3. For the compound \$\mathrm{CH_3COCH_3}\$, recognize that the carbonyl carbon is bonded to two carbon groups (methyl groups), indicating it is a ketone, not an aldehyde.
4. For the compound \$\mathrm{CH_3COOH}\$, identify the carboxyl group (COOH), which characterizes a carboxylic acid, not an aldehyde.
5. For the compound \$\mathrm{CH_3CH_2OH}\$, note the presence of an -OH group attached to an alkyl chain, indicating it is an alcohol, not an aldehyde. The aldehyde structure is \$\mathrm{CH_3CHO}\$, where the carbonyl carbon is bonded to a hydrogen and a methyl group.