VJC 2025 Carbonyl Compounds Notes

1 VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT JC2 H2 CHEMISTRY Carbonyl Compounds (Aldehydes & Ketones) _______________________________________________________________________________ LECTURE OUTLINE 1. Introduction 2. Physical Properties 2.1 Boiling point 2.2 Solubility in water 3. Laboratory Preparation 3.1 Oxidation of alcohols 4. Reactions 4.1 Reactions of the carbonyl group 4.1.1 Nucleophilic addition reaction of HCN 4.1.1.1 Reactions involving cyanohydrin 4.1.2 Condensation reactions 4.2 Reduction of aldehydes or ketones 4.3 Oxidation of aldehydes 4.3.1 With acidified K2Cr2O7 or KMnO4 4.3.2 With Tollens’ reagent 4.3.3 With Fehling’s solution 4.4 Tri-iodomethane formation 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 LiAlH4 and HCN (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 Lesson 1 2 Pages 1 – 9 10 – 14 Complete by 23 Feb 23 Feb scan this QR code to ask questions related to the lecture

2 1 Introduction (Nomenclature/Structure) • General formula of CnH2nO • Functional group is C=O • Include both (i) aldehydes, RCHO (where R = H, alkyl or aryl groups) and (ii) ketones, RCOR’ (where R, R’ = alkyl or aryl groups) aldehyde ketone • Carbonyl compounds are widely used in perfume industry (e.g. aliphatic aldehydes with 8 –13 carbon atoms have very pleasant floral odours and are used in feminine perfumery) • Nomenclature a) Aldehyde for linear chains containing only aldehyde functional group 1. count the number of carbon atoms in the chain 2. the ‘e’ of the –ane of the alkane with the same number of carbon atoms is replaced by ‘al’. Note that it is not required to number the position of the aldehyde as it is assigned position 1 within the chain. name structural formula skeletal formula methanal HCHO ethanal CH3CHO propanal CH3CH2CHO butanal CH3CH2CH2CHO pentanal CH3CH2CH2CH2CHO for branched chains or chains containing substituents (-OH, -NH2, -R (alkyl), -X (halide)) 1. find the longest alkyl chain, which is the parent chain, that contains the aldehyde group 2. assign the aldehyde carbon as carbon position 1 and name the parent chain 3. identify substituent(s) on the parent chain and include its position as prefixes to the name of the parent