2025 VJC Carbonyl Compounds Tutorial

15 Victoria Junior College JC2 H2 Chemistry Tutorial: Carbonyl Compounds Complete the following tables. 1. Preparation of aldehydes and ketones starting compound reagents and conditions product (CH3)2CHCH2CHO (CH3)2CHCH(OH)CH3 K2Cr2O7(aq), H2SO4(aq), heat 2. Reactions of aldehydes and ketones reaction type reagents & conditions organic product(s) [if any] for (CH3)2CHCH2CHO (CH3)2CHCOCH3 HCN(aq), NaCN reduction @condensation K2Cr2O7(aq), H2SO4(aq), heat or KMnO4(aq), H2SO4(aq) heat

16 #Tollens’ reagebt or Fehling’s solution, heat *I2, NaOH(aq), heat Remarks: @ 2,4-DNPH is used to identify the carbonyl C=O functional group in aldehyde and ketone # Tollens’ reagent and Fehling’s solution is used to identify aldehyde and aliphatic aldehyde respectively * Alkaline aqueous I2 is used to identify CH 3CH(OH)– or CH 3CO– structural unit in organic compounds Reduction of Aldehydes and Ketones 1 A fresh salad may contain the following compounds. X CH3CH2CH2CH=CHCHO, an aroma of tomatoes Y CH3CH2CH2CH2CH=CHCOCH3, a flavour of mushrooms Z CH3CH2CH2CH2CH=CHCH=CHCHO, an aroma of cucumbers If these compounds are all present in the ratio X : Y : Z = 2 : 2 : 1, and all are reduced by a solution of an excess of NaBH 4, how many hydrogen atoms would be incorporated on average per molecule? A 2.0 B 2.4 C 3.6 D 4.4 N10/I/2

17 Organic Synthesis 2 Suggest how the following transformation can be achieved from the following starting compound: Indicate reagents and conditions you would use for each step. [7] (a) (b) (c)

18 (d) (e) (f)

19 (g) Nucleophilic Addition Mechanism 3 The simplest amide, methanamide, HCONH2, can be dehydrated to hydrogen cyanide, HCN. HCONH2 → HCN + H2O (a) Draw the mechanism of the reaction between hydrogen cyanide and ethanal, CH 3CHO, to form 2-hydroxypropanenitrile, CH3CH(OH)CN. [2]

20 (b) In some circumstances, double bonds will undergo a nucleophilic addition reaction. By applying your understanding of the following concepts: (i) electronegativity; (ii) electronic and steric effects; (iii) delocalisation of electrons, suggest reasons to explain why the following reactions occur or do not occur. [3] N18/III/1(e) [modified] ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………….

21 Dis