In organic chemistry, functional groups are crucial for understanding the reactivity and properties of organic molecules. Consider the following compounds:
Compound 1: CH3CH2OH (ethanol)
Compound 2: CH3COOH (acetic acid)
Compound 3: CH3CHO (acetaldehyde)
Compound 4: CH3CH2NH2 (ethylamine)
Which of the above compounds contains a carbonyl functional group?