Chapter 18 · Organic Chemistry
18.14Aldehydes and Ketones
9 min · two checks
Predict
How do you tell an aldehyde from a ketone in a structure?
The idea
- Identify aldehydes and ketones.
- Name methanal, ethanal, and propanone.
The carbonyl group is C=O. Aldehydes are named with -al: methanal (formaldehyde), ethanal (acetaldehyde). Ketones are named with -one: propanone (acetone). Formaldehyde is used to preserve tissue. Acetone is a common solvent and nail-polish remover. Because the carbonyl is polar, these molecules have higher boiling points than alkanes of similar mass, and small ones mix with water. They do not hydrogen-bond to themselves unless something else in the molecule has an O–H.
Aldehydes oxidize easily to carboxylic acids; ketones do not, under the same gentle conditions, because there is no hydrogen on the carbonyl carbon. That difference is a laboratory test and a metabolic fact. In sugars, the words “aldose” and “ketose” mean the same distinction inside a carbohydrate.
Keep these
- Aldehyde: carbonyl at the end, named -al.
- Ketone: carbonyl between carbons, named -one.
- Aldehydes oxidize to carboxylic acids more readily than ketones oxidize.