Aldehydes and ketones typically exist in which form?

Aldehydes and ketones typically exist in the keto form because this structure is more stable compared to the enol form. The keto form has a carbonyl group (C=O) that directly participates in resonance with the surrounding atoms, contributing to its stability through the ability to delocalize electrons.

In contrast, the enol form, which features a hydroxyl group (−OH) adjacent to a double bond (C=C), is generally less stable due to the higher strain and lack of favorable resonance structures. While certain conditions can favor enol formation, such as in cases involving certain substituents or specific reactions, in general, the keto form predominates in the equilibrium between these two structures. This stability understanding aligns with the well-known preference for carbonyl-containing compounds like aldehydes and ketones to exist predominantly as ketones in their more stable keto form.