What is the classification of esters in terms of functional groups?

Esters are classified as non-terminal functional groups. This is due to their structural characteristics, which feature a carbonyl group (C=O) directly bonded to an oxygen atom that connects to another carbon chain or group. This structural arrangement places the ester functional group within the interior of the molecule rather than at the end, which is characteristic of terminal functional groups such as aldehydes and carboxylic acids.

Furthermore, esters typically do not exhibit the features of terminal or intermediates in the same way that functional groups like aldehydes or ketones do. Instead, they can be categorized as part of larger molecular structures, which is what makes them non-terminal. Thus, understanding esters as non-terminal helps to place them in the proper context of organic functional groups, where their reactivity and properties can be appropriately evaluated.