Which of the following compounds contains an ester functional group?

• A. $\mathrm{CH}{3}_{}-\mathrm{COO}-\mathrm{CH}{3}_{}$
• B. $\mathrm{CH}{3}_{}-\mathrm{COOH}$
• C. $\mathrm{CH}{3}_{}-\mathrm{CHO}$
• D. $\mathrm{CH}{3}_{}-\mathrm{CO}-\mathrm{CH}{2}_{}-\mathrm{CH}{3}_{}$

Answer: (A)

Verified step by step guidance

1. Identify the functional groups present in each compound by analyzing their structural formulas and characteristic groups.
2. Recall that an ester functional group has the general structure \(\mathrm{R-COO-R'}\), where a carbonyl group (\(\mathrm{C=O}\)) is directly bonded to an oxygen atom that is also bonded to another carbon chain.
3. Examine the first compound \(\mathrm{CH_3-COO-CH_3}\): it contains a carbonyl group adjacent to an oxygen atom connected to another carbon, matching the ester functional group pattern.
4. Check the second compound \(\mathrm{CH_3-COOH}\), which contains a carboxylic acid group, characterized by \(\mathrm{-COOH}\), not an ester.
5. Look at the third compound \(\mathrm{CH_3-CHO}\), which is an aldehyde with a carbonyl group bonded to a hydrogen, and the fourth compound \(\mathrm{CH_3-CO-CH_2-CH_3}\), which is a ketone with a carbonyl group bonded to two carbon atoms; neither are esters.