Which of the following pairs of molecules contain the same functional groups?

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

Answer: (C)

Verified step by step guidance

1. Identify the functional groups present in each molecule of the given pairs. For example, in CH\_3CHO, recognize the aldehyde group (-CHO), and in CH\_3COCH\_3, identify the ketone group (C=O within the carbon chain).
2. Compare the functional groups in each pair to see if they match exactly. Functional groups define the chemical properties, so molecules with the same functional group belong to the same functional class.
3. For the pair CH\_3COOH and CH\_3COOCH\_3, identify that the first molecule contains a carboxylic acid group (-COOH) and the second contains an ester group (-COO-). These are related but distinct functional groups.
4. Examine the pair CH\_3CH\_2NH\_2 and CH\_3NH\_2. Both contain an amine group (-NH\_2), although one is a primary amine with an ethyl substituent and the other is a methyl amine. Since both have the amine functional group, they share the same functional group.
5. Finally, analyze the pair CH\_3CH\_2OH and CH\_3OCH\_3. The first contains an alcohol group (-OH), while the second contains an ether group (-O-). These are different functional groups, so this pair does not share the same functional group.