SAJC 2026 Halogen Derivatives Self-Check (Tutors)

1 St Andrew’s Junior College H2 Chemistry 2025 Tutorial 13: Halogen Derivatives SELF-CHECK QUESTIONS Mechanism 1. Halogenoalkanes react with aqueous alkali. One mechanism of this reaction has the reaction pathway diagram shown below. Which statements are correct? 1 The reaction is an example of nucleophilic substitution. 2 Between X and Y the C-Hal bond will be lengthening. 3 The energy difference between X and Z represents the activation energy. A 1, 2 and 3 B 1 and 2 C 2 and 3 D 1 only Ans: A (1, 2 and 3) 1. True. OH− substitutes halogen in R-hal. 2. True. C−hal bond starts to break between X and Y and C−OH bond starts to form as well to reach the transition state in Z shown below: C R HO Hal H H 3. True. −

2 Reactions of Halogenoalkanes 2. Write balanced equations and the reagents and conditions for the following conversions. (a) CH3CH2Br to CH3CH2NH2 (1 step) CH3CH2Br + NH3 → CH3CH2NH2 + HBr Reagent & Conditions: NH3 in ethanol, heat under pressure (b) CH3CH2Br to CH3CH2COOH (2 steps) CH3CH2Br + KCN → CH3CH2CN + KBr Reagent & Conditions: KCN in ethanol, heat CH3CH2CN + 2 H2O + H+ → CH3CH2COOH + NH4+ Reagent & Conditions: H2SO4 (aq), heat (c) CH3CH2Cl to CH2(OH)CH2OH (2 steps) CH3CH2Cl + NaOH → CH2=CH2 + KCl + H2O Reagent & Conditions: NaOH in ethanol, heat CH2=CH2 + H2O + [O] → CH2(OH)CH2OH Reagent & Conditions: KMnO4(aq), NaOH(aq), cold (d) Benzene to 3-chloronitrobenzene (2 steps) Reagent & Conditions: Cl2, anhydrous AlCl3, heat Reagent & Conditions: conc HNO3, conc H2SO4, 50oC

3 3. The diagram shows a reaction sequence. What would be the product Q? Ans: D Nucleophilic substitution occurs to form a nitrile (the alkyl chain increases by 1 C). Nitrile is reduced to a primary amine. 4. The reduction of a nitrile produced a compound of formula C3H7NH2. Which compound would be produced if the same nitrile was hydrolysed by heating with dilute hydrochloric acid? A CH3CH2NH2 B CH3CH2OH C CH3CH2CO2H D (CH3)2CHCO2H Ans: C The primary amine produced is CH3CH2CH2NH2 which means the nitrile is CH3CH2CN. When CH3CH2CN undergoes acidic hydrolysis, it will become CH3CH2COOH. Ni heat

4 5. N16/1/25 Ans: D Rate of reaction 1 is higher than rate of reaction 2 because of the weaker C – Br bond. Lecture notes 4.2.1 → Down the group, size of the halogen atom increases and the valence orbitals of the halogen atom become bigger and more diffuse. Orbital overlap is less effective and C – X bond strength decreases. Less energy is required to break the C – X bond. Option A is wrong as Cl is more electronegative (F > O > Cl ~ N) Option B is wrong as Br− and Cl− ions are not electrophiles Although Option C is a correct statement, it cannot be used to explain the experimental results. If polarity were the main factor, a more polar C−Cl bond means the C in C−Cl has a larger 