Final answer:
The structure that represents a carboxylic acid from the given list is CH₃COOH, also known as acetic acid. It contains the -COOH functional group that characterizes carboxylic acids.
Step-by-step explanation:
The student has asked to identify which of the given structures represents a carboxylic acid. A carboxylic acid is an organic compound that contains the carboxyl functional group, which consists of a carbonyl group (C=O) attached to a hydroxyl (-OH) group, typically represented as -COOH. The nomenclature of carboxylic acids usually involves naming the parent compound by finding the longest continuous chain that contains the carboxyl group and then changing the -e at the end of the alkane name to -oic acid.
Among the structures presented:
- CH₃CH₂CH₂CH₃ - This is butane, an alkane.
- CH₃CH₂PH₂ - This is an alkyl phosphine, not a carboxylic acid.
- CH₃COOH - This is a carboxylic acid, specifically acetic acid.
- CH₃CH₂OCH₂CH₃ - This is an ether, not a carboxylic acid.
- CH₃CH₂OH - This is an alcohol, specifically ethanol, not a carboxylic acid.
Therefore, the compound CH₃COOH is the carboxylic acid in the list presented by the student.