What defines a carbonyl group?

A carbonyl group is specifically defined by the presence of a double bond between a carbon atom and an oxygen atom. This structure can be found in various functional groups, most notably in aldehydes and ketones. In aldehydes, the carbonyl group is at the end of a carbon chain, while in ketones it is located within the carbon skeleton. The carbonyl's characteristic double bond is significant because it gives rise to unique chemical properties that influence reactivity and interactions in biological molecules, such as sugars and fatty acids. Understanding the structure of a carbonyl group is crucial for studying organic compounds and their functions in biological systems.