RI Organic Remedial

Name: ………………………………………. ( ) Class: ……………. Date: ……………. Raffles Institution Year 6 H2 Chemistry 2025 Set A T2W7 – Halogen Derivatives, Hydroxy and Carbonyl Compounds Notes: Nucleophilic substitution mechanisms  Pre-ChemFocus Activity  • Familiarise yourself with the following mechanisms: Nucleophilic Substitution (SN1, SN2), Nucleophilic Addition • To view infopack at IVY > C2025 – H2 CHEMISTRY > Pages > [ChemFocus] Y6 T2W7 Halogen Derivatives, Hydroxy and Carbonyl Compounds > FIRST VIDEO

Self-Check Questions 1 When an optically pure solution containing 2 -chlorobutane reacts with NaCN under alcoholic conditions, the resulting solution was optically active. 2-chlorobutane Cl + CN - CN Cl -+ (a) A description of the reaction mechanism is illustrated below. Circle and annotate on the diagram to indicate how the mechanism is drawn incorrectly. C Cl CH3 H CH2CH3 δ-δ+ - CN NC C Cl CH3 H CH2CH3 C H CH3 NC CH2CH3 Cl - Learning points: (b) 2-chloro-2-methylbutane also undergoes nucleophilic substitution reaction with NaCN under alcoholic conditions. However, the overall order of reaction was found to be 1 instead of 2. Explain why. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………..[2] Check your answers at IVY > C2025 – H2 CHEMISTRY > Pages > [ChemFocus] Y6 T2W7 Halogen Derivatives, Hydroxy and Carbonyl Compounds > Remaining videos

2 (a) In the boxes A to F below, draw the structural formula of organic compounds formed. (b) In the table below, suggest the reagents and conditions for reactions (i) to (vi). Reaction Reagents and Conditions (i) (ii) (iii) (iv) (v) (vi) CH3CH2O-Na+ heat F B CH3CH2CH2OH CH3CH(OH)CH3 C E LiAlH4, dry ether Or H2, Ni, heat limited Br2 uv light KOH (aq) heat (v) A (ii) (iii) D CH3CH2CH2NH2 (iv) (i) KCN in ethanol, heat CH3CH2CH2Br CH3CO2H (vi)

3 Mark with a ( ✓) if the following compounds gives a positive test with each of the following chemical test. O 2,4-dinitrophenylhydrazine Fehling’s solution, heat Tollens’ reagent, heat I2(aq), NaOH(aq), heat O 2,4-dinitrophenylhydrazine Fehling’s solution, heat Tollens’ reagent, heat I2(aq), NaOH(aq), heat OH 2,4-dinitrophenylhydrazine Fehling’s solution, heat Tollens’ reagent, heat I2(aq), NaOH(aq), heat O 2,4-dinitrophenylhydrazine Fehling’s solution, heat Tollens’ reagent, heat I2(aq), NaOH(aq), heat O 2,4-dinitrophenylhydrazine Fehling’s solution, heat Tollens’ reagent, heat I2(aq), NaOH(aq), heat

Tutorial Discussion Questions (to complete before Chemfocus session) 1a A reaction scheme involving 2-bromopentane, CH3(CH2)2CHBrCH3, is given below. CH3(CH2)2CHBrCH3 2-bromopentane ethanolic KCN heat D (C6H11N) HCl(aq) heat E CH3(CH2)2CH(CH3)CH2NH2 H2, Ni, heat A student investigated the kinetics of the conversion of 2-bromopentane into D. The rate equation of the reaction was found to be: rate = k [2-bromopentane] [CN–]. The sample used in the reaction contained only the following isomer of 2-bromopentane. There was an inversion of configuration in this reaction. C Br H H3C CH3CH2CH2 (i) Describe the mechanism of the conversion of 2-bromopentane into D. Show relevant lone pairs, charges and dipoles, and use curly arrows to indicate the movement of electron pairs. You may represent 2-bromopentane as CH3CH2CH2–CHBrCH3. [3] (ii) Suggest a structure for organic product E. [1]

2a Carbonyl compounds such as ethanal react with hydrogen cyanide, in the presence of trace amount of sodium cyanide, to form cyanohydrins. (i) Draw the mechanism of this reaction. Show all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] (ii) For the following pair of compounds, describe one simple chemical test which would enable you to distinguish between them. State clearly how each compound behaves in the test. O and O OH O propanone 2-oxobutanoic acid ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………..[2] 3a Suggest two reasons why phenol has a larger Ka than cyclohexanol. ……………………………………………………………………………………………………… …………………………………………………………………………………………………..….. …………………………………………………………………………………………………..….. …………………………………………………………………………………………………...[2]

Tutorial Practice Questions (to be attempted IN CLASS) 1b Describe the mechanism for the reaction of bromoethane with ammonia, showing curly arrows, charges, dipoles and relevant lone pairs. [3] 2b (i) Describe the mechanism of the reaction between cinnamaldehyde and HCN with trace amount of KOH. O cinnamaldehyde [3]

(ii) The product mixture obtained at the end of the reaction was optically inactive. Explain why. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………..[2] 3b State and explain whether phenol has a larger pKa value than 2-nitrophenol. …………………………………………………………………………………………………..….. …………………………………………………………………………………………..………….. …………………………………………………………………………………………..………….. ……………………………………………………………………………………….…………..[2]

Self-Check Answers 1(a) 1(b) 2-chloro-2-methylbutane forms a stable carbocation with 3 electron donating groups which help to disperse positive charge on C. Hence, it undergoes SN1. Additionally, the 3 bulky alkyl chains hinders the approach of the nucleophile for backside attack, hence, it is unable to undergo SN2. C Cl CH3 H CH2CH3 δ-δ+ - CN NC C Cl CH3 H CH2CH3 C H CH3 NC CH2CH3 Cl - 1. Should show tetrahedral shape about Cδ+. 2. Should show backside attack δ Missing transition state symbol Missing δ– dipoles. Should show tetrahedral shape about C and inversion of

2(a) 2(b) Reaction Reagents and Conditions (i) excess conc NH3 in ethanol, heat in sealed tube (ii) KOH (aq), heat (iii) excess conc H2SO4, heat (iv) ethanolic KOH, heat (v) 1. cold conc. H2SO4 2. H2O, heat (vi) KMnO4(aq) , H2SO4(aq), heat 3 O ✓ 2,4-dinitrophenylhydrazine ✓ Fehling’s solution, heat ✓ Tollens’ reagent, heat I2(aq), NaOH(aq), heat O ✓ 2,4-dinitrophenylhydrazine Fehling’s solution, heat Tollens’ reagent, heat ✓ I2(aq), NaOH(aq), heat CH3CH2O-Na+ heat CH3CH=CH2 (F) CH3CH2CH3 (B) CH3CH2CH2OH CH3CH(OH)CH3 CH3CH2CH2CN (C) CH3CH2CH2COO-K+ Note: NH3 also formed LiAlH4, dry ether Or H2, Ni, heat limited Br2 uv light KOH (aq) heat (v) 1. cold conc H2SO4 2. H2O, heat (ii)KOH (aq) / heat (iii) excess conc H2SO4, heat CH3CH2CH2CH2NH2 (D) CH3CH2CH2NH2 (iv)ethanolic KOH heat (i) e