Aldehydes and Ketones: Nucleophilic Addition and the Four Tests

In the paper

Unit 3, Organic chemistry, carries 17 of the 50 chemistry marks — the heaviest unit in the subject; with eleven chapters sharing them, this one averages a little over one and a half (MEC publishes weights by unit, not by chapter). The carbonyl group is the hinge of the whole unit: the alcohols of Alcohols and phenols oxidise into it, and the acids of the next chapter oxidise out of it.

MEC scope: Nomenclature and isomerism; Preparation and chemical properties of aliphatic carbonyl compounds; Preparation and properties of benzaldehyde.

Three ways it is asked:

• Recall: what Rosenmund reduction uses; what Fehling's solution B contains; which reagent gives an orange precipitate with every carbonyl.
• Understanding: why acetone is less reactive than acetaldehyde towards a nucleophile; why benzaldehyde gives Tollens' test but not Fehling's; why formaldehyde cannot undergo the aldol reaction.
• Application: identify a compound from a set of test results; predict the aldol product of a given aldehyde; decide whether a named carbonyl gives iodoform.