What is the prefix used for aldehydes?

The correct prefix for aldehydes is "oxo-," which indicates the presence of a carbonyl group (C=O) at the end of a carbon chain. Aldehydes are defined by their functional group, which consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydrogen atom, denoted as -CHO. The prefix "oxo-" can be used to indicate this carbonyl group in the case where the aldehyde functional group is not the highest priority or when naming more complex molecules that may have other functional groups.

This usage is particularly important in IUPAC nomenclature, where "oxo-" is applied to specify the carbonyl when it does not serve as the principal functional group. In contrast, while "keto-" refers to the carbonyl group found within ketones (which occurs in the middle of carbon chains), "carboxy-" describes the carboxylic acid functional group (-COOH), and "hydroxy-" is used for alcohols to denote the presence of a hydroxyl group (-OH).

Understanding these prefixes helps clarify the structure and reactivity of organic molecules in the context of their functional groups.