SAJC 2026 Halogen Derivatives Discussion (Students)

1 St Andrew’s Junior College H2 Chemistry 2026 Tutorial 13: Halogen Derivatives DISCUSSION QUESTIONS Mechanism 1. 2017/P3/Q5(c) – Modified The following scheme shows a synthesis of the beta-blocker drug, metoprolol. Study Fig 5.1 carefully and answer the questions that follow. (a) Name the mechanism of the reaction in each of the steps 1, 2 and 6. (b) Suggest the identity of the reagent T in step 5. (c) Suggest the identity of the reagent U in step 7.

2 2. 2016/P1/Q38 What could be formed during a nucleophilic substitution reaction? A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only 3. 2022/P1/Q22 The following scheme represents the result of a hydrolysis reaction. Which statements about this reaction are correct? 1 An intermediate in the reaction has a plane symmetry. 2 There are two intermediates in the reaction which are mirror images of each other. 3 The reaction proceeds via the SN2 mechanism. A 1, 2 and 3 B 1 only C 2 only D 3 only

3 4. Describe the mechanism of the alkaline hydrolysis of CH 3CH2CH(CH3)Br. Explain why the resulting organic product(s) would be optically inactive. In your answer, show any relevant charges, dipoles or lone pairs of electrons you consider to be important in this mechanism. 5. 2019/P3/Q4(c) When phenylethene reacts with HC l(g), only one of the two possible constitutional (structural) isomers with formula C 8H9Cl is formed. When this isomer, E is reacted with NaOH(aq), compound F, C8H10O, is produced in a reaction whose rate is independent of [OH–(aq)]. (a) Draw the structures of the two possible constitutional (structural) isomers of C8H9Cl that could be formed from phenylethene. [1] Criteria of Success for SN1 mechanism:  Name of mechanism: Nucleophile Substitution, SN1  δ+ on C, δ– on X  Curly arrows to show flow of a pair of electrons  Lone pair of electrons on Nu−  Trigonal planar carbocation intermediate  Nu− attack from either side of the trigonal plane  Label slow and fast steps  If chiral C exists, a pair of optical isomers as products

4 (b) Identify isomer E, and draw the structure of F. [1] (c) By referring to the mechanisms of these reactions, explain why both E and F are produced as a 50:50 mixture of enantiomers. [2] Reactions of Halogenoalkanes 6. 2022/3/4f (a) Describe the mechanism for the reaction of 1 -bromopropane with hot ethanolic NaCN. Show relevant lone pairs of electrons, dipoles and curly arrows. [3] Criteria of Success for SN2 mechanism:  Name of mechanism: Nucleophile Substitution, SN2  3D representation of reactant and product  δ+ on C, δ– on X  Lone pair of electrons on Nu–  Nu– attack from the side opposite to X  Curly arrows to show flow of a pair of electrons  Bond