2021 YIJC Prelim P3 QP

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper Additional Materials: Data Booklet 9729/03 13 September 2021 2 hours This document consists of 34 printed pages. For Examiner’s Use Section A 1 /21 2 /25 3 /14 Section B 4 /20 5 /20 Penalty /80 READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question.

2 ©YIJC Section A Answer all the questions in this section. 1 5-bromo-4-methyl-3-penten-2-ol can be made from 5 -bromo-4-methyl-3-penten-2-one in one step. The molecules are labelled as A and B respectively in Fig. 1.1. Fig. 1.1 (a) (i) State the total number of σ and π bonds in a molecule of A. [1] (ii) Describe the hybridisation of the orbitals and the bonds between the carbon atoms of the C=C double bond in A. [2] (iii) State the total possible number of stereoisomers that can be exhibited by B. [1] (iv) Sodium borohydride is used to reduce A to form B. Explain why only the ketone functional group in A undergoes reduction with sodium borohydride but the alkene functional group does not. [2] (v) Describe a chemical test that can be used to distinguish A and B. [2] …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………..

3 ©YIJC [Turn over …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………..

4 ©YIJC Compound E can be made from A by a four-step synthesis. Fig. 1.2 (b) (i) Suggest the reagents and conditions for steps 2 and 3 in Fig. 1.2. [2] (ii) Compound E is neutral and does not react with 2,4 -dinitrophenylhydrazine or sodium metal. Draw the structures for compounds C, D and E. [3] (iii) 5-chloro-4-methyl-3-penten-2-ol can be used as the reactant in step 2 instead of B in the reaction scheme in Fig. 1.2. Suggest how the rate of reaction will change if 5-chloro-4-methyl-3-penten-2-ol is used. [2] …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………..

5 ©YIJC [Turn over …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………..

6 ©YIJC (c) The Cannizzaro reaction is a base catalysed reaction, which involves the disproportionation of aldehydes to form a carboxylic acid and an alcohol. 2RCHO → RCOOH + RCH2OH The mechanism of the Cannizzaro reaction involves 4 steps. A nucleophilic attack on the carbonyl carbon of the aldehyde produces a dianion via a 2-step process. In step 3, the dianion reacts with another aldehyde molecule to form the carboxylate and alkoxide ions. In step 4, both the carboxylate and alkoxide ions are protonated to form the products. (i) Define the term disproportionation, with reference to the Cannizzaro reaction. [2] (ii) In step 1 of the mechanism, the OH– ion acts as a nucleophile and attacks the carbonyl carbon to form an intermediate. In step 2, the second OH – ion abstracts a proton from the hydroxyl group on the intermediate to form the dianion. Showing any relevant lone pairs, dipoles and charges, indicate the movement of electrons with curly arrows to outline the mechanism involved in the first 2 steps of the Cannizzaro reaction. [2] (iii) Deduce the products of the reaction when benzaldehyde undergoes the Cannizzaro reaction. [2]

7 ©YIJC [Turn over …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. [Total: 21]

8 ©YIJC 2 (a) This question is about compounds of Group 17 elements and period 3 elements. (i) Using data from the Data Booklet, state and explain how the thermal stability of the Group 17 hydrides vary down the group. [3] (ii) Describe the reactions, if any,