RI 2019 Prelim P3 QP

1 © Raffles Institution 2019 9729/03/S/19 [Turn Over RAFFLES INSTITUTION 2019 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9729/03 Paper 3 Free Response 26 September 2019 2 hours Candidates answer on separate writing paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. 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 a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer one question. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely together, with the cover page on top. The cover page is found on page 2. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 16 printed pages.

2 © Raffles Institution 2019 9729/03/S/19 [Turn Over RAFFLES INSTITUTION 2019 Year 6 Preliminary Examination H2 Chemistry Paper 3 COVER SHEET Name: ( ) Class: For Examiner’s Use Only Question Marks Section A 1 / 20 2 / 20 3 / 20 Section B (Circle the question you have answered) 4 / 20 5 / 20 Total / 80 Attach this cover sheet to your writing paper.

3 © Raffles Institution 2019 9729/03/S/19 [Turn Over Section A Answer all the questions in this section. 1 Aminoketones are often used in the synthesis of drugs. (a) The antidepressant, bupropion, is a drug which contains an aminoketone. The final step in the synthesis of bupropion involves the reaction between compound G and an amine. (i) Write an equation for the reaction to form bupropion from compound G, showing clearly the structure of the amine used in the reaction. [1] (ii) Explain why compound H was not formed in the reaction. [3] compound H (iii) Describe a simple chemical test to distinguish between compound H and bupropion. [2] A different aminoketone is prepared by the reaction between 2-bromo-1-phenylethanone and triethylamine. 2-bromo-1-phenylethanone PhCOCH2Br The rate of the reaction between PhCOCH 2Br and triethylamine was investigated by the following method. This is Experiment 1. Equal volumes of 0.10 mol dm −3 PhCOCH2Br and 0.10 mol dm −3 triethylamine were placed in a water bath at 30 C. Both solutions were prepared in an organic solvent. After thermal equilibrium, the two solutions were mixed and kept at constant temperature throughout the reaction.

© Raffles Institution 2019 9729/03/S/19 [Turn Over 4 After one minute, a 5.0 cm 3 aliquot of the reaction mixture w as collected and added to 10.0 cm3 of sulfuric acid. The resulting mixture was analysed by titration. The procedure was repeated at different time intervals. (b) (i) Why was the aliquot added to sulfuric acid? [1] (ii) Why was it necessary for the PhCOCH2Br and triethylamine solutions to be kept at the same temperature before the start of the reaction? [1] (iii) Explain, with the aid of a diagram, how changing the temperature of the reaction to 60 C would affect the rate of the reaction. [2] (c) A graph of the results of Experiment 1 is given in Figure 1.1. Figure 1.1 Determine the initial rate of the reaction. [1] 0 0.01 0.02 0.03 0.04 0.05 0.06 0 100 200 300 400 time / min [triethylamine] / mol dm−3

© Raffles Institution 2019 9729/03/S/19 [Turn Over 5 (d) Further experiments were carried out using the same method with varying concentrations of the reagents at 30 C. Experiment [PhCOCH2Br] / mol dm−3 [triethylamine] / mol dm−3 relative initial rate 1 0.10 0.10 1 2 0.10 0.05 0.5 3 0.05 0.05 0.25 Deduce the rate equation for the reaction and state the units of the rate constant. [2] (e) Based on your rate equation, name and draw the mechanism for the reaction between 2-bromo-1-phenylethanone and triethylamine. Show relevant lone pairs and dipoles, and use curly arrows to indicate the movement of electron pairs. Represent 2-bromo-1-phenylethanone as PhCOCH2Br and triethylamine as R3N. [3] (f) Experiment 1 was modified by replacing PhCOCH 2Br with other reagents. The reactions proceed via the same mechanism as in part (e). In each case, state whether the initial rate of the reaction is higher or lower compared to Experiment 1. Give reasons for your answer. (i) 0.10 mol dm−3 of PhCOCH2I. [1] (ii) 0.10 mol dm−3 of compound G. [1] (iii) 0.10 mol dm−3 of (2-bromoethyl)benzene. [2] [Total: 20]

© Raffles Institution 2019 9729/03/S/19 [Turn Over 6 2 There is a growing interest in using iodine and its compounds in research due to their unique and interesting physical and chemical properties. (a) Iodine is the first element of group 17 that exists as a solid at room temperature. Explain why. [2] 2-Iodoxybenzoic acid (IBX) is used in organic syntheses to carry out unconventional reactions. The structure of IBX is shown below. (b) IBX is an example of a chemical species which exhibits hypervalency – the ability of an atom in a molecule to hold more than 8 electrons in its valence shell. (i) Identify the group 17 element(s) which is/are unable to exhibit hypervalency and explain why the element(s) is/are unable to do so. [2] (ii) The iodine atom in IBX is surrounded by five regions of electron density arranged in a trigonal bipyramidal shape. A trigonal bipyramidal arrangement is shown below. Draw a clear diagram of IBX w ith an arrangement of atoms around iodine, including lone pairs of electrons if any, which would result in the most stable structure. Briefly explain why the chosen arrangement is the most stable. [2]

© Raffles Institution 2019 9729/03/S/19 [Turn Over 7 (c) A common use of IBX is to oxidise primary alcohols to aldehydes and secondary alcohols to ketones. In the process, IBX is converted to iodosobenzoic acid (IBA). (i) State the change in the oxidation state of iodine when IBX is converted to IBA. [1] (ii) Alcohol J (C8H16O) is optically active and is one of four stereoisomers. When an excess of IBX was added to J, K (C8H10O) was obtained unexpectedly as the product. Furth