Carbonyl Compounds

Content

● Aldehydes (exemplified by ethanal)

(i) oxidation to carboxylic acid

(ii) nucleophilic addition with hydrogen cyanide

(iii) characteristic tests for aldehydes

● Ketones (exemplified by propanone and phenylethanone)

(i) nucleophilic addition with hydrogen cyanide

(ii) characteristic tests for ketones

Learning Outcomes

Candidates should be able to:

(a) describe the formation of aldehydes and ketones from, and their reduction to, primary and secondary alcohols respectively

(b) describe the mechanism of the nucleophilic addition reactions of hydrogen cyanide with aldehydes and ketones

(c) explain the differences in reactivity between carbonyl compounds and alkenes towards nucleophilic reagents, such as lithium aluminium hydride and hydrogen cyanide

(d) describe the use of 2,4-dinitrophenylhydrazine (2,4-DNPH) to detect the presence of carbonyl compounds

(e) deduce the nature (aldehyde or ketone) of an unknown carbonyl compound from the results of simple tests (i.e. Fehling’s and Tollens’ reagents; ease of oxidation)

(f) deduce the presence of a CH3CO– group in a carbonyl compound from its reaction with alkaline aqueous iodine to form tri-iodomethane