ASRJC 2025 H2 Chem Carbonyl Compounds Notes

2025 J2 H2 Carbonyl Compounds ©2025/ASRJC/CHEM 1 ANDERSON SERANGOON JUNIOR COLLEGE JC2 H2 CHEMISTRY CARBONYL COMPOUNDS Guiding Questions 1. How are carbonyl compounds synthesised? 2. Which class of reagents do carbonyl compounds react with and why? What types of reactions do carbonyl compounds undergo and why? 3. How do carbonyl compounds react with HCN in nucleophilic addition? 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 References 1. Chemistry for Advanced Level, Cann and Hughes, Murray 2. A–Level Chemistry by E.N. Ramsden 3. Understanding Chemistry for Advanced Level by Ted Lister and Janet Renshaw 4. Chemistry in Context by Graham Hill and John Holman Part I: Introduction A. The carbonyl group B. Aldehydes and ketones Part V: Reactions A. Nucleophilic addition reaction Mechanism for nucleophilic addition of HCN B. Reduction reaction C. Oxidation reaction D. Condensation (addition–elimination) reaction Part II: Nomenclature A. Naming aldehydes B. Naming ketones Part III: Physical Properties A. Boiling points B. Solubility Part IV: Preparation of aldehydes and ketones Oxidation of alcohols Part VI: Chemical tests A. Distinguishing carbonyl compounds B. Distinguishing aldehydes only C. Distinguishing aldehydes and ketones with CH3CO– group

2025 J2 H2 Carbonyl Compounds ©2025/ASRJC/CHEM 2 (A) The carbonyl group  The carbonyl group, C O, is present in aldehydes and ketones. Bonding in the carbonyl group:  and  bond in carbonyl group OC R' R  bond C O R' R  bond p orbital  The carbonyl carbon is sp2 hybridised and forms three  bonds, which are planar.  The unhybridised p orbital of the carbon atom overlaps sideway with the adjacent p orbital of the oxygen atom to form a  bond. Comparison between alkene and carbonyl group Alkene Carbonyl even electron density in alkene electron density pulled closer to electronegative carbonyl oxygen  Electron cloud is evenly distributed between the tw