The functional group present in an aldehyde is
- A. a hydroxyl group
- B. a carbonyl group at the end of the chain, written CHO
- C. a carboxyl group
- D. a carbonyl group between two carbon atoms
Explanation
In an aldehyde the carbonyl carbon carries at least one hydrogen and so must be terminal, whereas in a ketone the same carbonyl group lies between two carbon atoms. This structural difference is why aldehydes are readily oxidised to carboxylic acids and give a positive test with Tollens reagent while ketones do not. The carboxyl group of an acid combines a carbonyl and a hydroxyl on the same carbon.