What is the IUPAC name for CH3-CH2-C(=O)-OH?

The compound CH3-CH2-C(=O)-OH contains a carboxylic acid functional group, indicated by the presence of the -C(=O)-OH structure. The longest carbon chain that includes the carboxylic acid functional group consists of four carbon atoms, which corresponds to butanoic acid.

To derive the IUPAC name, one must first identify the longest continuous chain. In this case, there are four carbon atoms in total, leading to a base name of "butanoic acid." Given that the carboxylic group takes priority and is always numbered as carbon 1, this confirms that the compound should be recognized as butanoic acid rather than any other option available.

In terms of the other options, propanoic acid would only be appropriate if there were three carbons and the same functional group, which is not the case here. Ethanol, on the other hand, is an alcohol and lacks the carboxylic acid functional group, while propanal is an aldehyde, which also does not apply given the presence of the carboxylic acid group. Therefore, the IUPAC name for CH3-CH2-C(=O)-OH is butano