Where does an aldehyde typically appear in a carbon chain?

An aldehyde is characterized by the presence of a carbonyl group (C=O) bonded to a hydrogen atom and is typically found at the end of a carbon chain. This structural positioning is essential for distinguishing aldehydes from other carbonyl-containing compounds, such as ketones, which have their carbonyl group located in the middle of the carbon chain.

In organic nomenclature, aldehydes are named by taking the name of the longest carbon chain containing the aldehyde group and modifying the suffix to "-al" to indicate its presence. Importantly, this functional group is terminal—meaning it can only reside at one end of the carbon chain and not within it, making option B the correct description of where an aldehyde typically appears.

Thus, the end placement of the aldehyde group plays a crucial role in its chemical reactivity and the properties of the molecules in which it is contained. This positioning is foundational in organic chemistry, particularly in the study of functional groups.