Question

Which of the following is an aldehyde?

• A. CH₃–CO–H (acetaldehyde)
• B. CH₃–CH₂–CO–CH₃ (butan-2-one)
• C. CH₃–CH₂–CO–CH₂–CH₃ (pentan-3-one)
• D. CH₃–CO–CH₃ (acetone)

Hint:

An aldehyde has an H on the carbonyl carbon (–CHO); ketones have two carbons on it.

Answer 1

The Correct Option is A

Step 1: The test for an aldehyde is the presence of the terminal –CHO functional group (a hydrogen directly on the carbonyl carbon).
Step 2: Scan the structures for an H on the C=O carbon. Only CH₃–CO–H shows the pattern R–CO–H, where R = CH₃ and one bond is to hydrogen.
Step 3: The remaining three species have the carbonyl carbon sandwiched between two alkyl groups (R–CO–R'), the signature of a ketone.
Step 4: Therefore the aldehyde is \[ \boxed{CH_3CHO} \] i.e. option (i).