Understanding condensed structures in organic chemistry is crucial for identifying functional groups and their properties. For ketones, the condensed structure is represented as COC, which can sometimes be presented as C(=O) to indicate the presence of a carbonyl group. This notation helps clarify that there is a double bond between carbon and oxygen. It's important to differentiate this from ethers, which are denoted as ROR. In ethers, both carbon atoms are typically bonded to hydrogen atoms, while in ketones, the carbon adjacent to the carbonyl does not have any hydrogens attached. Thus, when you see CO, it signifies a ketone, indicating that the carbon is bonded to a carbonyl group without hydrogens.

On the other hand, aldehydes are represented by the condensed structure CHO. This abbreviation can be particularly confusing, as it does not intuitively suggest its functional group. A mnemonic to remember this is to think of "choo choo train," which can help in memorizing that CHO corresponds to an aldehyde. It is essential to commit this to memory, as many students often forget this association, especially in advanced organic chemistry courses. Therefore, extra attention should be given to aldehydes to avoid confusion with other functional groups.